Fortification

FORTIFICATION

FORTIFICATION is the art of strengthening, by works of defence, positions in which it is proposed to place troops so as to render them secure from the attack of an enemy. Such positions may contain within them towns, dockyards, arsenals, and ports, or may serve merely for shelter for an army in the field; but the object to be attained is always the same, and the works of defence are so disposed round the position that, while they offer the greatest obstacles to the advance of their assailants, they afford the utmost shelter to their defenders. Fortification is, in short, the art of enabling the weak to resist the strong.

Various terms have been adopted in connexion with the general term of Fortification, but none of them are of much use in considering the subject, and some may lead to error, by inducing the engineer to restrict himself under some circumstances to a very limited view of his subject. Thus, Fortification Natural and Fortification Artificial implyause-less distinction, as every engineer must avail himself of the natural advantages or obstacles of ground, as well as of the obstacles his science and genius enable him to add to them; and thus in every Fortification nature and art must act together. Fortification Regular and Fortification Irregular are defective terms, as no Fortification can possibly be regular unless it should so happen that the ground it occupies, as well as the ground surrounding it on all sides, is uniform in level and general character. Again Fortification Permanent and Fortification Field or Temporary have reference only to the immediate object of the works, or to the application of the science, and in no way affect its principles, which remain the same whether the work is a simple earthen intrenchment, or a great fortress surrounded by masonry walls. Fortification Offensive and Fortification Defensive are, however, of all terms the most objectionable, since they imply a contradiction to fact, for the perfection of defence depends as much on its active offensive operations as on the protection of its covering works, while the perfection of attack depends as much on the skill with which its passive protective works are pushed forward as on the fire of its batteries.

The principles of Fortification then should be studied unshackled by any of these distinctions, and the engineer should apply his means to his end, using without restriction the works best suited to his purpose; and it is in this way that the study of the subject will be here treated.

Elementary Fortification.

It is desirable to examine the exact meaning of technical words, in order to acquire a distinct notion of the ideas they were intended to convey, and to obtain a glimpse of the historical progress of the science in which they are used. Fortify, Fortifications, Fortress, Fort, are all derived from fortis, strong; and the idea the first two convey is that, by artificial arrangement, additional strength is bestowed upon one combatant over another, or upon one party of combatants over another party. A rock, the trunk of a tree, a bank of earth, or any natural object, which shelters the body of a man from the missiles of his opponent whilst it leaves him free to discharge his own, may be considered the simplest form of fortification.

A bank of earth, when reduced to the requisite thickness, and moulded into proper form, with such slopes as the particular tenacity of the earth may require to insure stability, or which the intended direction of the fire over its summit may render necessary, becomes a Parapet, so called from the Italian words para, a defence or guard, and petto, the breast, or, in English, a breastwork. If the Breastwork or Parapet be made only sufficiently high to permit the soldier to fire over it, he will be exposed after firing, and will be forced to crouch in order to obtain cover. The parapet is therefore made high enough to cover the soldier when standing up so that he can load with ease and security, and can move with safety from place to place behind it. This increased height renders it necessary to introduce a Banquette or step (accessible by an easy slope), standing upon which the soldier can fire over the parapet and from which he can retire by the interior slope to the lower ground behind it; the name Banquette is derived from banchetta, a little bench or step. As Parapets are usually formed artificially, the earth for their construction is derived from a ditch, which being dug immediately in front of and parallel to the parapet, forms by its depth an additional obstruction to an advancing enemy. Ordinary intrenchments are formed of a simple parapet and ditch, but in more important outworks and in fortresses the height is further augmented by elevating the parapet on another mound of earth called the Rampart {riparo in Italian), and as this additional height requires a greater quantity of earth, the ditch is made both wider and deeper. By these means the difficulties of attack are increased, additional cover is given to the magazines or other buildings within the fortress, and the command over the country is raised and improved in efficiency, by elevating the soldier so that he can see over the many minor obstacles which would otherwise restrict his field of view.

Some writers, regarding the presence or absence of the rampart as the main distinction between permanent and temporary works, have proposed to call the former Rampart or Town Fortification, the latter Parapet or Field Fortification; but this distinction is not of universal application, and the more ordinary divisions of Permanent and Field Fortification better indicate the nature of the works and the objects for which they are intended.

In order to study efficiently the combinations of these simple elements, with a view to form from them works of defence, it is necessary that we should know the manner in which such works are represented on paper. As in architecture, of which in earlier times fortification was only a military branch, this is effected by the plan, the section, and the elevation, of which the first two are the most important. The plan of a work is the orthographic projection of the lines of intersection of the planes of its slopes on the plane of construction. The elevation is a similar projection on a vertical plane. The section or profile is made on a plane perpendicular to the lines of intersection of the planes or slopes, and therefore represents the traces of these planes on the sectional plane. Fig. 1 represents a small portion of a simple parapet in plan and profile, and leads to the following explanation of terms :—

In the plan, cc represents the crest of the parapet or highest ridge line of the work. In delineating the outline of a work, it is this line which is always drawn; it is called the “trace.” Between cc and ce is the superior slope; between ce and a line parallel to it through s is the exterior slope, prolonged in this case to the bottom of the ditch dd, being continuous with the escarp sd; gg is the crest of the glacis, or ridge of a slightly elevated mound of earth raised on the exterior edge of the ditch, or counterscarp, and sloping gently outward, so that the assailants passing over its surface may be in the prolongation of the superior slope of the parapet, and therefore in the line of fire from its crest; by its elevation the glacis increases the amount of descent into the ditch. Within the crest of the parapet are seen the interior slope of the parapet, bounded by b'b', the banquette, between b'b , and bb, and the interior slope of the banquette, bounded by aa. Relief— This term is adopted to indicate the height of any point of the work either above the plane of construction, which is sometimes the plane of site, when it is called constructive relief, or above the bottom of the ditch, when it is called absolute relief. The absolute relief is a very important datum, as it expresses the total obstruction offered by the parapet and ditch to the ascent of the assailant, and it has a bearing on the regulation of the length of lines, which mutually defend each other. The Relief of a work is the relief of the crest of its parapet The Command of a work is the height of the crest of its parapet, either above the plane of site if horizontal, or above any point of that plane specially referred to, or above the crest of the parapet of any other work in front of it; the difference of height, therefore, between the crest of the parapet in fig. 1 and the crest of the glacis is the command of the parapet over the glacis; in the one case the command is absolute, in the other relative.

But after all a simple parapet and ditch afford only temporary protection, and it is necessary to stop an enemy as he advances to them by placing obstacles in his path which shall retain him as long as possible under the fire of the works opposed to him either in front or in flank. In the profile in fig. 1, the simplest form of such an obstacle, viz., a Palisade, is shown. When, however, in combination with direct fire only, as in the figure, palisades check an enemy but for a short time, and are principally useful as affording more time to the defenders. Indeed in any combination of defence palisades are now of much less value than formerly, as they are readily destroyed by indirect fire, and by the new explosives which are more portable and far stronger than gunpowder; they are mainly used in closing the gorges of temporary works. Many other obstacles may, however, be so arranged as to assist materially in rendering simple direct fire more effective.

Abattis are formed of trees cut down, and arranged side by side with the branches interlaced outwards, and the stems inwards; the branches should be freed from foliage, and their ends cut sharp. They may be arranged in one or more rows, so that the fire from the parapet shall sweep along their summits, their stems being firmly fastened by pickets to the ground and partly buried in it; an enemy would suffer great loss whilst attempting to remove them underfire. The best abattis are formed of good-sized growing trees. The trunks are partially cut through a little above the ground, and the trees are bent down and securely fastened to the ground and to one another by pickets and iron wire.

Fig. 2 exhibits an arrangement of Abattis; and it will be observed that in this profile the exterior slopes of the parapet and the escarp are formed into one gentle slope, whilst the counterscarp retains its ordinary slope. By this modification the difficulty of descending into the ditch remains as before, and the sloping pickets in front of the abattis prevent the assailants from clearing it away. In simple inclosed works, such as redoubts, and in lines, the defence frequently depends on direct fire alone; and in these cases a work of the profile here figured with obstacles would be far more effective in checking an enemy than a work of ordinary profile without obstacles, and would render it impossible that a watchful garrison should be surprised; and this is a very important consideration, as a vigorous and bold enemy could scarcely be stopped if he had succeeded in arriving at the foot of the escarp unchecked.

Fig. 3 exhibits another arrangement formed only of large branches securely picketed down to the ground. In this case the form of the ground is taken advantage of, and the profile of the defensive line is modified, a trench being cut out behind it, and the banquette being formed on the surface of the ground. By simple arrangements of this kind, it will often be possible to carry defensive lines over a large extent of ground in a short period of time, and to obtain more effective defence by taking advantage of the natural facilities of the ground than by the construction, with a great expenditure of labour and time, of elevated works, not so well fitted to sweep the surface of the ground, ward or pulled downhill backward, and securely fastened by chains to the ground or to upright posts, they form a very formidable obstacle.

Fraises are palisades placed in a horizontal or nearly horizontal position. They are of wood or iron, and are usually made about 10 feet long and 15 inches thick, bound together by two ribands, nailed above and below them and buried in the ground, without which they would be more easily torn away. They are fixed both on the counterscarp and on the escarp. When on the escarp, they are inclined downwards, and the berm is cut away; when on the counterscarp, they are inclined upwards. On the counterscarp they are safe from direct fire, and retain an enemy outside the ditch.

Fig. 5 represents, in section, a row of fraises on the escarp. In this profile the ordinary banquette for musketry is represented by dotted lines below a wider terreplein, formed for artillery to fire over the parapet, or “ en barbettef as it is usually called; but this will be more fully explained below.

The “Wire Entanglement” is the best and most easily made of hasty accessory defences. It can be applied everywhere, and can be made by anybody; the material of it is carried in a small compass; it does not interfere with the fire of the defence; it cannot be seen from a and to act upon the obstacles placed to check the progress of the assailants.

Chevaux-desrise.— The Cheval-de-frise (fig. 4) is a substitute for an abattis. It consists of a strong horizontal beam, 12 feet long and 9 inches square, through which are passed strong lance-like rods of wood or iron, sharp at both ends, and about 6 inches apart. Several of these may be joined together by rings and hooks with which the ends of the beams are fitted.

Chevaux-de-frise require a considerable amount of skilled labour in their construction; hence they can only be employed in limited quantities for limited objects. They are employed for temporary purposes, e,g., as barriers to the entrance of a work, across a road or street, in positions where they can be easily removed when the communication is required to be used. They have the disadvantage of being removed or destroyed without much difficulty. It is, however, usual to keep as articles of store iron chevaux-de-frise, so made that the parts are separable for convenience of package and transport. If planted at the bottom of a hollow, exposed to direct fire, so that they must either be pushed uphill for-

distance; and artillery has little effect upon it A form of wire entanglement is shown in fig. 6. Stout stakes are driven into the ground 5 feet apart, and disposed in rows chequer-wise; strong wires are wound round them about 1 foot 6 inches above the ground, crossed diagonally by finer wires. No entanglement should be less than 3G feet in depth. The wires should hang slackly from their supports, as when strained they are easily divided by a swordblow, and the stakes should vary in height. 14 B.W.G. steel wire is very suitable for the thicker wires; it is strong and weighs only 90 ft> per mile. Wire entanglements in the bottom of a ditch offer a strong resistance. They are well placed in the slopes of the glacis and counterscarp and on the berm; but they are most effective when interwoven with bushes and trees in the defence of woods.

Iron “band Gabions,” when disposed as in fig. 7, form a good entanglement. The bands are buttoned and placed in lines 4 feet apart, and connected together by strong wires passing through the bridging holes.

Crows' Feet (fig. 8) are made of iron with four points so arranged that one shall always project upward in whatever manner they may be thrown on the ground; the points are either 2 or 4 inches long. Crows’ feet are sown over a space about 12 feet broad. Troops coming suddenly, and in the dark, on these obstacles, would be much annoyed by them. They are most effective against cavalry, and were formerly much used,—more so than now.

Trous-de-loup are holes in the ground in the form of an inverted cone or square pyramid, the sides of which are as steep as is consistent with the stability of the soil. They are made 6 or 8 feet in diameter and 6 feet deep, so that an enemy cannot use them as shelter pits to fire from. At the bottom is fixed* a sharp stake 3 feet long, or the branch of a tree cut into sharp points, or a number of smaller sharp pickets, or a quantity of crows’ feet. Fig. 9 shows, in plan and section, the arrangement of trous-de-loup proposed by Wenzel.

If along the line of a position, either on the glacis or on the escarp (when gradually sloped as in fig. 2), small trees or shrubs are planted, they can be on an emergency cut down, and with the points of their stumps sharpened they would become very annoying to an assailant. Harrows and many other substitutes can also be used; indeed every expedient which ingenuity can suggest should be adopted by the engineer to check the progress of an advancing enemy, and to delay him as long as possible under fire.

Stockades.— Before proceeding to the investigation of the principles which should regulate the relief and thickness of ordinary parapets, viewed in reference to simple defensive lines and to direct fire, it is right to notice the “Stockade” as a substitute, and in some circumstances an advantageous substitute, for a parapet. The Stockade is formed of one or more rows of stout palisades, and in its simplest form is thus constructed. A row of very strong palisades, usually pointed at the top, from 9 to 12 inches in diameter, is fixed deeply in the ground, with intervals of about 3 inches between the palisades. These intervals are filled by smaller palisades cut square at the top—every alternate palisade being shortened 4s inches, so that the open space above it may be used as a loophole. A stout riband nailed horizontally to the upper ends of the palisades strengthens the construction materially.

Such a Stockade is shown in plan, elevation, and section in fig. 10; it has a banquette of earth, which may be replaced when desirable by a wooden step. By cutting out the triangular portion shown in the section, and throwing the earth up against the front of the palisades, as indicated by the dotted lines, an exterior slope and escarp are formed which keep an enemy constantly in view. A stockade of this description placed close to the edge of a steep bank, has this great advantage over a parapet, that the men behind it have a more effective command of the ground before them when firing through the loopholes than they could possibly have when firing over a parapet. It is here supposed that artillery fire cannot act directly against the stockade, but artillery may possibly be placed to act against it in a longitudinal direction, or, as it is termed, to enfilade it, and in this case the line of stockade should be interrupted by traverses, which are usually banks of earth placed transversely to the line they are intended to protect from such artillery fire. Fig. 11 shows a stockade of this description applied to the defence of precipitous ground. When stockades are formed into inclosed works, they are called “Tambours.”

Under some circumstances it may be desirable to throw an ordinary parapet forward to the edge of a bank, the slope of which supplies the function of escarp, and hence to dig the ditch behind instead of before it, as in fig. 12, where it will be also observed that the slope of the banquette is broken into two steps, the tenacity of the earth when first excavated allowing it to stand firm; the principle of this excavated form of structure is adopted in sunken batteries. Sometimes the object of the parapet is merely cover and not active defence, in which case the banquette is omitted as in fig. 13, and the work is called an “Epaulement.” In this profile it will be observed that a space is left between the face of the epaulement and the internal ditch. Such a space should always be left, whether the ditch is within or without, when the work to be formed is of any considerable elevation, as it affords a stage upon which the builders can stand, and lessens the height to which the diggers have to throw the earth from the ditch; it is very important to keep this space clear by throwing forward or backward the earth as quickly as it is raised. The distinguishing characteristic of an able engineer is the power of varying his appliances—thus in his hands the abattis may become the fraise, or may take the place of the palisade, as in fig. 14. If this be not borne in mind, evil rather than good may result from adherence to systematic instruction; as the engineer who has acquired a knowledge of one contrivance may be found crippled by his constant efforts to conform to it rather than to seek some other better fitted to the circumstances of the case. In this profile a berm is represented, as it would be difficult to arrange the abattis and to build the parapets without it.

The arrangement of the trous-de-loup, combined with stakes driven into the ground is shown in fig. 15, an advanced glacis having been formed of the earth thrown out of the excavations. The ditch is in this case triangular; and it is scarcely necessary to add that the particular form of ditch must be determined by the nature of the ground, remembering that the contents of the ditches must supply material for the parapets; and their depth, as it adds to the difficulty of assault, should not be diminished except from necessity.

After these preliminary remarks, the student should be prepared to enter on the consideration of Field Fortification.

Rules for determining the Dimensions of Parapets. Determination of the Relief of a Parapet.— First, where the ground is horizontal,—for the protection of troops in a normal position. The minimum for a simple parapet may be here stated at 6 feet 6 inches, as a musket ball would penetrate the parapet for a few inches below its crest, and the maximum at 8 feet, a height which gives the defenders perfect security under almost every circumstance of fire, including that from mounted soldiers.

Defilade.— Secondly, where the ground is uneven, and it is necessary to defilade the work from a point or points which command it.

Fig. 16 explains the first case, in which the points A, B, C, are on the same level, the distance AB being the space intended to be protected by the parapet at C. The line CF represents the supposed normal height at which it is presumed the assailants may fire, in this case 8 feet; BE will be the same; and AD cut by the line drawn from F to E will be 8 feet.

In fig. 17, A, B are still considered to be in one horizontal plane, but C is considerably elevated; and hence, adopting the same data as to height, and drawing the line FE and the line OB parallel to it, AD, or the height of the parapet, is equal to AI + ID,—ID l>eing equal to BE, or CF, or N, the normal height. Calling also AB, or the distance to be covered, d ; AH, or the distance from the commanding point, D; and HC, or the height of C above A and B, H,—we have Al: HC :: AB: HB; or Al: H :: d : <Z + D; and hence AI-jA.H,.ndAD-N+^.H . . . (1); so that the necessary height of the parapet increases as the height of the commanding point increases, or as the distance AB to bo defiladed increases, and diminishes as the distance from the commanding point increases. Taking D = 600 ft., d = 30 ft., H = 60 ft., then Al —or 2 ft. 10 in., and AD, the height of the crest of the parapet =8 ft.'+ 2 ft. 10 in.—10ft. 10 in.; or taking D —1200 ft., or 400 yards, then AD = 9 ft. 6 in.

Fig. 18 represents A lower than B by a quantity —AO — GH—ä; hence AD - AO + OI + ID, and OI - θ⅞⅞9 _ —É_, (H-Λ),or BG D + a

AD-N + Λ +π ⅛-. (H-Λ) (2); D + d ' ’ which shows that the deeper A is sunk below B and C the more elevated must be the parapet, and hence that this is a very unfavourable condition of parapet. For example, let A be 2 ft. below B, and all other data the same as before, then y ∙ . (∏ - ħ) — 2 ft. 9 in., D+rf ' 7 and AD = 8 ft.+2 ft. 9 in.+ 2 ft.— 12 ft. 9 in.; or when D≈1200 ft., AD— lift. 4 in.; and if it should be necessary to defilade a distance of 90 ft. instead of 30, the heights of the parapet would necessarily become 18 ft. 8 in., and 14 ft. 2 in.

Again, in figure 19, A is higher than B, and C is lowest of all; and if H still represents the difference of level of A and C, and h the. difference of level of A and B, then

AD≡N-A- i ⅛. (H-ä) (3); D + d and, of course, so far as concerns the height alone of the parapet, this is the most favourable condition of all.

Any other case is easily resolvable by one or other of the formulae;—thus, when A and C are on the same level, and B higher than A, H is 0, and equation (2) becomes AD — N + - . Ä.

And in equation (3), if B be higher than A, ħ becomes positive, and AD=N + Ä-p^· (H+ a ) (4); or if Abe 0, A and B being on the same level, AD = N - jj^∙ h ∙

In equation (4), if the station C, though below A and B, falls between the horizontal line drawn through A and the line BR, or BA be prolonged till it cuts the surface of the ground sloping from B towards D, then . (H + h) is less than h, and AD is greater

D + α

than N; but should C be below the line BR, then -st . (H + Λ) 1) + d is greater than ^h, and AD is less than N; or, in other words, should the line of defilade passing through BA meet the ground at R within the prescribed limite of defilade, or the effective ranges of musketry and artillery, which may be now assumed as 800 yards for the first and 3000 yards for the second, then if the point C be above that line the parapet at A must be made higher than the normal height, and if below it may be made lower. A comparison of the examples under equation (2) will exhibit the great disadvantage to the defenders of simple lines of having any ground near to their own moderately elevated, and care should be therefore taken either to occupy such ground or to throw back the lines opposite to it as far as possible, and, should it have the character of a ridge, to bring some portion of the fire of the lines to act in the direction of its length. The space AB to be defiladed must depend upon circumstances; the minimum, to allow safe communication for the troops behind and actually defending the parapet, ought not to be less than 30 feet, but when it is necessary to draw up troops behind the parapet it ought not to be less than 90 feet; in cases of double lines or of inclosed works the distance must of course vary, as the object will be to protect, not only the troops near to the enemy from a direct fire, but the troops arming the more distant parapet from a reverse fire. In assuming the normal height as 8 feet, on the supposition that protection is required from the fire of mounted soldiers, a condition is assumed which is not generally likely to occur in the attack of intrenchments. Nevertheless, the command of a work should be sufficient to cover the defenders standing on the ground inside. Infantry are assumed to be 6 feet high, and to protect them, within a reasonable distance of the parapet, from projectiles clearing the crest and tending downwards in the latter part of their trajectory, the command of a parapet on level ground should be at least 8 feet. Shrapnel fire being effective at 3000 yards, and the elevation of the heaviest gun of position for a range of 3000 yards being 7°, the balls clearing an 8-feet parapet will strike the ground 18 yards in rear of the crest of the parapet. In equation (3), and in one case of (4), as explained, the height of the parapet becomes less than N, but should the diminution extend so far as to reduce the height of the parapet below 7 feet, the relief should be restored to its proper amount by excavating the ground behind the parapet, or, in other words, forming a terrepleine below the level of the plane of site. In a similar manner, in equation (2), and in one case of (4), where the parapet becomes greater than N, it would be very inconvenient to augment the height above 12 feet, and it is preferable therefore to excavate behind the parapet, whenever the defilade requires so great an increase of height.

In the preceding observations the parapet has been considered as a simple straight line, deriving its defence solely from its own direct fire; but such a condition would most frequently be found inapplicable, in respect of form, in consequence of the natural inequalities of the ground, and unsatisfactory, in respect of defence, in consequence of the imperfect operation of direct fire from the top of a parapet, which can strike the ground in front only in the prolongation of its superior slope, leaving everything within this defenceless; the line in which the superior slope meets the ground is called the “Limiting Line of Defence.” A disposition of trace has therefore been adopted by which the fire of one portion of the parapet takes in flank an enemy advancing directly against the adjoining portion; and a work is said to be flanked when the arrangements are such that an enemy cannot advance against any portion of it without being taken in flank by the fire of some other portion. In lines of intrenchments this arrangement leads to a bent line, having angles projecting towards the exterior called “salient angles,” and angles retired from, the exterior called “re-entering angles’’; and it is evident that in this arrangement the lines AB and AC (fig. 20), which are flanked by BD, CD, in their turn flank BD and CD; such flanking defence is called “reciprocal defence.”

Referring back to the subject of defilade, it is evident that a bent line of this kind affords more facility for defilade than a straight line, as it is often possible so to arrange the position of the angles that the salients shall occupy higher ground, while the re-entering angles, though placed lower, shall be compensated for this disadvantage by being further removed from the commanding ground of the enemy.

Though a simple straight line has the disadvantage of depending for its defence solely on direct fire, it is not exposed to be swept along its whole length by an enemy’s fire. Fire of this kind is called “enfilade” fire, and is very destructive; it produces the same effect upon the defence as flanking fire upon the attack, viz., it takes the defenders of the line in flank. To guard against this evil, should it be necessary to take up a position in front of ground of a superior command, the long lines AB, AC (fig. 20) should be so directed that then prolongations may fall on low ground at E, F, and not as they would do in the case of AB', AC', on the high ground at E', F'; and, if possible, as where the high ground is not continuous the prolongations of both short and long lines should fall on low ground between the commanding eminences, an arrangement which will be especially advantageous should the low ground be marshy or otherwise difficult of occupation by an enemy. Such observations as these are only suggestive, since no fixed rules can be laid down to meet all cases. The engineer should examine the ground and adjust his works so as to make the most of its advantages, and to neutralize, as far as possible, its disadvantages. To determine the height of the parapet by the rules for defilade formulated above, it is necessary to have a correct plan of the ground, and to know the exact levels of the points A, B, C, in every case; but where there is no such plan, the defilading may be effected in practice by levelling poles or boning rods. In this case, the inner boundary of the ground within the parapet to be defiladed being staked out, a boning rod of 7 or 8 feet high, according to the intended normal height of the parapet, should be placed at Bon the staked-out line, and anotherof equal height on the commanding point or ground C (fig. 21), supposed to be at a distance equal to the range of the projectiles from the fire of which the work is to be defiladed. A rod about 12 feet high is then fixed at A, and a cross piece or marker is raised up or down it until it meets the point where the visual line from the top of B to the top of C intersects the pole at A; this operation is simply the mechanical determination of the height obtained in the other method by calculation. If it be required to defilade the whole space between two parallel lines, or that included between the two lines forming the salient angle in fig. 20, it is evident that the work must be defiladed from both sides, and further, that the soldiers standing on the banquette of one line should be secured from the fire of the ground in front of the other, which firo is called reverse fire, because it strikes them in rear. This ⅛ effected by placing a mound of earth or traverse between them, and determining its height as well as the height of the parapets in the following manner :—

On the commanding point C (fig. 21) is placed a boning rod CD of the normal height, and another BE of the same height at B, or at the position of the traverse; then the height of the crest of the parapet of A is determined by the intersection of the visual line from D to E with the pole fixed at A, at the point a, which is here high, as C is so much higher than A. See preceding rules and equations. In like manner a pole of the proper height being fixed at the extent of range on the opposite side at C', the visual line from D' to E determines the height, a', of the parapet of A', which is much lower than the parapet of A, as A'and c' are nearly on the same level. Now, to defilade the banquettes, and to determine the height of the traverse necessary for that purpose, set up on the banquette of A a pole δδ of the same height as CD, C'D', BE, and the visual line from D ’ to δ determines the height of the traverse at ∕, which is necessary to secure the banquette of A from the reverse fire of C', whilst the visual line drawn from D to b' determines the height of the traverse sufficient to protect the banquette of A' from the reverse fire of C.

The application of these principles to a work formed of two lines (or “faces” as they are called), terminating in a salient angle is shown by fig. 22, but the application is the same whether the work is connected with a line of intrenchment as a “redan,” is detached as in a “ravelin” and other outworks, or forms part of a peculiar system or arrangement of works, as in the tenaille system of Montalembert, called by its author the angular system,—terms and works which will be hereafter more fully explained. Here the commanding point is supposed to be at Μ, and to secure the defenders of the face AB from a reverse fire it is necessary to interpose the traverse cd, called from its object a “parados.” The length of the traverse cd, is determined by the line MB, beyond which it should project sufficiently to give ample security to a space about 50 feet wide behind the parapet. At the other end, the traverse is not carried up to the salient angle, as it would interfere with the communication, but is completed by ba, perpendicular to the other face, by which arrangement the space within the salient and the banquette are left free. The two lines M√B and Me/, passing through points at the normal height above the banquette, determine the height of the traverse. It may, however, happen that the commands are so situated as to give an enfilade fire along both the faces AB, AB' (fig. 23). In this case a small work DAD' is formed in connexion with the parapet, by drawing lines parallel to the crests CB and C'B' at a distance from them equal to the breadth of the banquette, and then determining, in the manner explained, the heights at A necessary to defilade a certain length of the banquettes of CB and C'B' from the fire sweeping them, and assuming the greater of the two as the height of the parapet at A. This work is called a bonnette; and when the height necessary to defilade the whole of one or both faces is found to exceed 12 feet, the height of A should be restricted to that limit, and traverses T, T', T 2 should be placed at such distances as shall defilade the remainder of the work.

The internal space may frequently be sufficiently defiladed by raising the salient portion of the parapet without disturbing the line of direction of the crest; but in that case the banquettes of the two faces would not be covered from enfilade fire, and hence the necessity of a bonnette. The increased height of the parapet of the bonnette renders it necessary to adopt two banquettes b, b', one below the other, and each provided with steps to facilitate ascent (figs. 23,24). The operation of defilading may be also effected by planes of defilade; as, for example, if the line which marks out or limits the space to be defiladed be first drawn, and a plane be supposed to pass through a line either 6 ft. 6 in. or 8 ft. (or whatever height between these may be assumed as the normal height N) above the limiting line, and through a point the same height above the commanding point, this plane will determine the height of the parapet, the crest of wshich will necessarily be in it.

Where the parapet is continued not only on the flanks but also in rear, so as to form an inclosed work, it may often be necessary to defilade it in various directions as in fig. 25. Where two traverses or parados cross each other, they must, of course, be so placed that they shall not only completely defilade the whole interior space of the work, but shall secure from reverse fire the banquette on each side, the normal N being therefore at least 6 ft. 6 in. above the banquette. Where traverses of this kind become necessary, the engineer must take in to account the space they will occupy, and plan his work accordingly; and should he be able to render the difficulty of attacking one side of his works very great, he may construct the traverses so that they may be used as retrenchments, and thus increase the means of defence; for example, S being the salient of greatest strength, bcb might be defended, and then bed.

This subject has been enlarged upon because it is of much importance in military engineering, as the safety of a long line of works may be endangered by defective defilade. Though considered here in a practical form, it depends entirely upon geometrical principles, and instruction in descriptive geometry is therefore essential in all schools of military engineering.

Having determined the relief of the crest of the parapet in reference to the plane of site, all the other vertical dimensions follow from it, as shown in several of the preceding figures; whilst the horizontal dimensions are determined by the thickness necessary to resist the enemy’s missiles and by the slopes required to ensure stability. The Penetration at a mean range into common earth after it has been dug up and well-rammed and into other materials is as stated below, and to these dimensions one half should be added for the thickness for security.

English Field Artillery. [table]

English Rifled Small Arm. [table]

. The penetration into sand is about two-thirds the penetration into earth, and about one-half that into clay.

The penetration into oak is about half that into fir.

With light, sandy, or gravelly soil, or, when ramming can only be imperfectly performed, greater thickness should be allowed; and as a wide and deep ditch must always materially strengthen the work before which it is placed, there can be no reason other than want of time, want of men, or difficulty of ground, for reducing the thickness of the parapet below 14, or at the utmost 12 feet. For forming the parapet under peculiar circumstances of difficulty the engineer will avail himself of every fitting substance which may be at hand, such as bags of wool, mattresses, fire-wood, manure heaps, and fascines, either by themselves or packed in gabions. The resistance of fascines is not great, their strength being rapidly diminished by the speedy fracture of their branches when exposed to sharp fire.

With these data it will be easy to regulate all the dimensions of the parapet,—the height of its crest, or the relief of the work, having been first established. Thus the banquette or step on which the men stand, when firing over the parapet, should for convenience be 4 ft. 3 in. below the crest. The breadth or tread should for a single rank be 3 ft., for a double rank 5 ft.; the surface should slope backwards 2 inches in the 3 ft., 3 inches in the 5 ft., so as to discharge water freely and keep the banquette dry; the base of the interior slope of the banquette up which the men mount should be twice its height; if the height of the parapet exceed the normal height, the banquette should have two treads or steps, the lower about seven feet below the crest, so that one rank of men may stand thereon whilst reloading the muskets of the rank on the step above them; or it should have three steps, each with a rise of 1 ft., and a tread of 1 ft. or 1 ft. 3 in., sloping slightly to the rear, by which arrangement the necessary excavation of the ditch will be diminished, and less of the interior space occupied. The interior slope of the parapet should be made very steep, so that a man firing over the parapet should be as close to it as possible; the base should not exceed one half the height; the superior slope, or “plongée f of the parapet, by which the fire is directed towards the point on which it is to act, should not be less than one-ninth, nor more than one-fourth of its thickness, and in service is generally made one-sixth; but as the increase of the slope facilitates the destruction of the crest, it should be kept as slight as possible. It is usual on the Continent to retain the angle of the crest, as a constant quantity, at 100°, and to increase the base of the interior slope as the plunge increases, and vice versa ; but this is not satisfactory, since, the height of the soldier’s shoulder remaining constant whilst the line of plunge varies, the fire will not be always in the true direction; and it is preferable to keep the base of the interior slope as small as possible, and to make the top of the parapet at the crest horizontal for one or two feet, commencing the plunge therefrom, but reducing the top as the plunge increases. This flat top will facilitate the use of sand bags (bags filled with earth), which are sometimes so arranged on the crest of the parapet as to form loopholes for the musketry, thereby adding to the cover of the men. The base of the exterior slope of the parapet should at least equal its height, though possibly in some soils— e.g. i chalk—the exterior slope may stand at a steeper angle than 45°. The slopes of the escarp and counterscarp should be as steep as practicable, but generally they will be the same as the exterior slope. Between the exterior slope and the escarp a “berm” is left. This berm is a space at least 1 ft. 6 in. wide and slightly inclined downwards and outwards for drainage; it gives greater stability to the exterior slope and to the escarp, prevents the earth from the exterior slope from falling into the ditch, and is a standing ground for the repair of the parapet. Where steeper slopes are indispensable, the earth must be retained in place by a wall called a “revetment,” which may be formed of fascines (long cylindrical faggots), hurdles, sods, planks, clay puddling, and, in the interior of works, of sandbags. The base of the interior slope of the glacis should be equal to its height, and the exterior slope should have aslope of 1 in 12. The command of the crest of the parapet over that of the glacis should be such that an assailant, standing on the crest of the latter, should not be able to fire into the interior of the work,—a condition which requires a command over the glacis of 5¾ feet, so that with a parapet 7 feet high the maximum height of glacis would be 1⅜ feet. The minimum height of the glacis is determined by another condition, viz., that the fire from the parapet should pass at no greater distance than 2 feet above its surface; and in no case should the plunge or slope of the glacis be greater than that of the parapet. An advanced glacis is sometimes adopted either to render the cover more effectual, or to occupy a favourable line for first opposing the progress of the enemy. Fig. 26 shows this arrangement, gg l , being the first or ordinary glacis, and <7 2 y 3 the second or advanced glacis, The slope of these glacis should not be such as to withdraw the assailants from the grazing fire of the parapet, and if it be not possible to extend the slope of g 2 g 2 so far as to keep it in the prolongation of the line eg 2 , it should be so arranged that no point of the slope should be more than 2 feet below that line or the plane corresponding to it, namely, the plane passing through the crest of the parapet and the crest of the advanced glacis. To form the advanced glacis, the slope at g is prolonged below the surface of the ground to g 1 , the earth excavated in doing this supplying the material for the glacis. When it is intended that the defence of this advanced glacis shall be derived solely from the parapet, either an abattis or rows of stakes may be placed immediately behind it, so as to stop the advance of the enemy when at the point of maximum exposure, but advanced glacis may often assume the character of successive intrenchments, and be defended with vigour and success. This figure will be again referred to when treating on defence by mines. The height of the parapet being determined by the amount of cover required, and the thickness by the nature of projectile to which it is exposed, the whole profile or section is necessarily completed on the principles pointed out, and the bulk therefore of earth contained in any portion of the parapet will be equal to the area of the mean or average profile multiplied by the length of that portion. Now, as this earth must be obtained from the ditch, the dimensions of the latter depend on those of the former'; and the volume of any portion of the excavated ditch will also be equal to the mean section of that portion multiplied by its length.

If, therefore, P represent the area of the mean section of this portion of the parapet, D the area of the mean section of the corresponding portion of the ditch, and L the length of this portion, then LP = LD, provided the earth be of the same bulk after as before excavation; but this is not the case, for after having been broken up from its previously closely packed condition, it is found that the “remblai” or earth built up exceeds the “déblai” or earth excavated by a coefficient varying with the nature of the soil, being in sandy soil nearly 0. Thus if — represent the coefficient, in sand it is 0, in earth of medium tenacity ∙⅛, and in very strong and naturally compressed earth ⅜; so that to render the earth of the ditch just equal to that of the parapet, the above equation should beLP - L (D ÷è I> )“dP - D +¾I>, orD- s ½ i P. As, however, the earth resulting from this excess, even allowing for the greater length of the ditch in polygonal works, will be required for forming the glacis, or for making up the banks, called “barbettes,” in the salients constructed for raising guns sufficiently high to fire over the parapet, the dimensions of the ditch may be safely estimated without reference to the excess, as follows :—

Let x be the breadth of the bottom of the ditch, and y its depth: and let the sum of the bases of the slopes of the escarp and counter scarp be represented as a function of the depth by the fraction ~ s y ∖ then x + 1 -y will be equal to the breadth of the ditch at top, and D = γr(x + x + - y ∖ ; whence x » − _ Ly, and y = a ∖ s j y as -( -χ+ . ∕ae 2 + —D )∙ Now, as the defensive object of rhe r∖ z y s ∕

ditch requires that it should be both deep and wide enough to form a decided obstacle to an enemy, the width ought not to be less than 18 feet, whilst the depth should have no other limit than that arising from the difficulty of raising the earth, which τ fixes 12 feet as about the maximum. Taking y — 12 feet, - =∙ S , and D≈108 square feet, then x=9-9 = 0, and the width of the ditch therefore “⅜ of 12 = 18 feet,—the ditch being triangular.

Assuming a profile area of 70, corresponding to a parapet 7 feet high and~only 6 feet thick, and making z=0 for a triangular ditch, √2 s

— D = 9 ft. 7 in., and the width of the ditch = 14⅛ feet; with a profile area'of 116 feet corresponding to a parapet 7⅜ feet high and 12 feet thick, the depth of the ditch, if triangular, is 12⅜ feet, and the width 181 feet; so that this profile appears about the maximum for a triangular ditch with a profile area of 163 feet, corresponding to a parapet 8 feet high and 18 feet thick. With a banquette 4 J feet wide a triangular ditch would give y =14% feet, so that such a form would be inconvenient; but taking x=4 feet as the width of the bottom of the ditch, y or the depth becomes 12 ft. 4 in., and the width of the top of the ditch 22⅛ feet—a very well-proportioned ditch.

In the preceding cases the base of the slope of the escarp has been assumed as equal to its height, and that of the slope of the counterscarp as equal to half its height. Should the nature of the soil be such as to require the base to be equal τ to the height in both escarp and counterscarp, -y = 2y; and should the soil be sufficiently firm to admit of a base of τ one-half in both, -y = y. In the first of these cases, even with the large profile area last named, the ditch may be made triangular with a depth of l2¾ feet, and a breadth of 25 feet; and in the second a triangular ditch is inadmissible with a profile area of 116 feet, as the depth would be more than 15 feet; indeed it would be inadmissible with profile areas beyond 85 square feet, for which a depth of 13 feet would be required. Before leaving this subject, a few words may be said respecting the “berm.” The most effectual escarp for defence is that which forms one continuous plane with the exterior slope, or at least which commences immediately where the other ends, as the absolute relief of the parapet is then a maximum, and there is no berm; but in many cases it would be imprudent to carry the parapet to the edge of the escarp, as injury to the latter would occasion the fall of part of the parapet, while the difficulty of construction would be greatly increased by having no intermediate stage between the bottom of the ditch and the top of the parapet. The “berm,” or step between the top of the escarp and the bottom of the parapet, is made from 1 foot 6 inches to 4 feet wide, according to the nature of the soil, and it then becomes possible in some cases to increase the slope of the escarp to a base of one-half or two-thirds, or at least to such a slope as shall place the foot of the escarp in the prolongation of the exterior slope of the parapet. The berm is encumbered with obstacles to prevent an enemy from making use of it as a halting place (see fig. 14). The slope of the counterscarp is usually one-third, one-half, or two-thirds, when that of the escarp is one-half, two-thirds, or 1; the bottom of the ditch should slope from the sides to the centre, to carry off the water, and obstacles should be provided there to prevent the enemy from collecting and reforming his men in the ditch, which, in all cases of simple lines, without flanking defences, he would do were it left free from obstructions.

Field Fortification.

The parapet has been hitherto considered principally in its character as the simplest element of defence, affording at once protection to the soldiers behind it and obstructing the advance of their enemies; but it is now time to consider the manner in which this parapet may be so arranged as to constitute a series of defensive and mutually defending works. If the antiquity of an invention be estimated by its position in the social history of the races of mankind, there can be no doubt that earthworks claim the priority over other forms of defence. In North America vestiges of circular earthen intrenchments, as well as of works of other forms, have been discovered, the antiquity of which is unknown; and in more recent times small parties of the aboriginal inhabitants encountering greater numbers of a hostile tribe have been known to excavate hollow spaces in the ground, and, throwing out the earth, to form around them circular intrenchments in which they have defended themselves to the last. In Ireland the ancient inhabitants have left similar relics of their earthen defences; in Great Britain there are numerous similar remains, the works of the Romans and of people long antecedent to the Romans; but the consideration of earthen works for the defence of extensive positions will be resumed further on, and such works will be considered here only in connexion with the arrangements adopted by an army in the field for its own immediate security.

The art of constructing temporary works in the field for this purpose is called Field Fortification. This art is of very high antiquity; the Roman soldiers relied much upon such works, and executed them with wonderful rapidity, even in the presence of an enemy.

Shelter Trenches.— Of this art the simplest form is that in which troops are preserved intact until the moment of attack arrives. At first sight it would seem that this can best be effected by keeping them out of fire. The increase in the range of arms of all kinds has, however, become so great that it is no longer possible to keep troops out of fire and yet in a sufficiently advanced position from which they shall be able to attack promptly; hence it has become an absolute necessity to provide shelter for them.

A very shallow trench with the earth thrown to the front will afford, to men lying in it, cover against artillery fire, and a good rest for their arms when they have occasion to deli√er their own fire. Moreover, it presents no obstacle to the advance of supporting troops, and offers but little mark to the enemy. Such trenches (figs. 27, 28, 29, 30) are called shelter trenches, and may be made of any depth or form according to the time and means available. They are very difficult of capture by the front attack, when defended by trained troops with breech-loading rifled arms, and can be quickly developed into regular intrenchments. The ordinary forms of shelter trench in use in the British army are show n in figs. 28, 29, and 30.

The Russians made use of shelter trenches with great effect in the defence of Sebastopol, and since that siege their employment has steadily developed.

In more recent times the greatest use of hasty intrenchments, though perhaps in the form rather of a line of intrenchments than of shelter trenches, was made by the Americans in the war of secession. Wherever they halted, no matter how short the time at their disposal, they threw up shelter. Each man worked for himself, and as if by instinct, and before fires were lit or provisions cooked, an intrenchment of some kind was formed. Probably the Americans had acquired this habit in their campaigns against the neighbouring Indians; and no doubt the superiority of rifled small arms, then for the first time freely used, thoroughly imbued them with a sense of the value of the slightest protection. General Sherman’s campaign in Atalanta, and the actions in the neighbourhood of Richmond and Petersburg, furnish numerous instances. With reference to them General Barnard reports that a simple trench defended by two ranks of foot soldiers is an obstacle unassailable by direct attack. General Wright relates that, attacking a handful of infantry, in single rank, behind a parapet and trench, with two divisions in line, the number of his casualties exceeded the number of the enemy, and that if the intrenchment had been defended by two ranks of good troops, a whole army corps would not have taken it; and in summing up his relation, he says that a simple trench, defended by two ranks of foot soldiers, covered by abattis and other obstacles, placed so that the new rifled arms have full scope, is absolutely impregnable except by surprise.

After the fall of Nicopolis in August 1877, 28 battalions of Turks, numbering about 10,000 men, collected at Plevna, and at once commenced to form shelter trenches; they were very deficient in artillery. Krüdener attacked them four daysafter with 7000 Russians and 30 guns, and was defeated with a loss of 2800 men. Ten days later he again attacked with 30,000 men and 170 guns, but in the meantime the Turks had thrown up several redoubts, and had so extended their shelter trenches that their position was beginning to assume the condition of an intrenched camp; moreover, their strength had been swelled by reinforcements to 45,000 men. The Russians were again defeated with a loss of 8000 men. Six weeks later, upon the 30th September, Krüdener, who had received 30 siege guns, having shelled the Turkish position for four days previously, attacked a third time with 50,000 Russians and Roumanians; but the Turks had in the interval received reinforcements of 10,000 men, and he was a third time repulsed with a loss of 15,000 men, though the Roumanians obtained possession of and held a large redoubt called Gravitza. It then became evident to the Russians that Plevna could not bo taken by assault, and they commenced to besiege by rule. By the 24th of October they had completed the investment by the occupation of the Loftcha and Rahova roads, all of which were previously open to the Turks, and had brought into battery against it 300 guns, 40 of which were siege guns. By the 10th of December they had collected 110,000 men and 500 guns around Plevna; and shortly after, Osman Pacha, having been repulsed with a loss of 6800 men in an attempt to cut his way out, surrendered, and his whole force, amounting to 43,000 men and 70 guns, became prisoners of war.

An army intrenched or fortified in the field is in many respects of the same effect as a fortress; the intrencħments supply the lack of numbers, and enable it to cover a country, to stop the advance of a superior enemy, or, if he chooses to risk a battle, oblige him to engage at a disadvantage. Charles V. furnishes a notable instance of the first. Opposed to a combined force of twice his strength, he at once commenced to intrench his army. In a few hours he was in a position to resist attack; in ten days he was so secure that, upon receiving reinforcements a few days later, he was enabled to assume an offensive which led in four months to the termination of the campaign in his favour, “In a war of march and manoeuvre,” says Napoleon, “if you would avoid a battle with a superior army, it is necessary to intrench every night, and to occupy a good defensive position. The natural positions which are ordinarily met with are not sufficient to protect an army against superior numbers without recourse to art. Those who proscribe lines of circumvallation, and the assistance which the science of the engineer can afford, deprive themselves gratuitously of an auxiliary which is never injurious, always useful, and often indispensable.”

Whenever Napoleon had time and occasion for strengthening his position by field-works, he acted upon the principles recommended in the above extract, as almost all his predecessors had done. In the wars which followed the Revolution of 1688, in those of Queen Anne’s reign, and during the Seven Years’ War, we find the commanders of each period, William III., the duke of Marlborough, Marshal Villars, Marshal Saxe, Frederick IL, and Marshal Dann, practically exemplifying their conviction of the great utility of field-works. Seven redoubts thrown up overnight saved Peter the Great at Pultowa, and enabled him to gain a decisive victory over his formidable antagonist; and at Borodino, three redoubts and eight flèches thrown up hastily by the Russians, caused the French great loss, and rendered the victory, which they gained by incredible efforts of gallantry, fatally costly; and it is not improbable that if the main redoubt had been closed at its gorge the French would have failed to take it. In 1761 Frederick the Great, having only 55,000 men to oppose to the united Austrian and Russian forces of 130,000 men, intrenched himself in the strong position of Bunzelwitz, in Upper Silesia, not far from Schweidnitz, which he held until the united armies were forced to retire for want of supplies. It has been argued by some that intrenchments and field-works have oftener been carried than successfully defended, and that hence incommensurate importance has been attached to them. But it should be remembered that victory in such circumstances has been purchased at an expense which has often rendered it in effect equivalent to defeat, and that a practice which the greatest commanders of ancient and modern times have approved and followed cannot be of doubtful utility. At Austerlitz, where the contending armies were nearly equal, Napoleon was preparing to superintend the construction of intrenchments when he found himself called upon to receive battle; and in Portugal, the duke of Wellington showed to what account the art of the engineer might be turned for influencing, not merely the fortune of a campaign, but the fate of a cause. The lines of Torres Vedras, which the powerful French army under Masséna was unable to pass, and from which the wave of war was rolled back broken into Spain, were perhaps the most remarkable works of the kind ever constructed.

“Lisbon,” says Sir John Jones, “being situated at the extremity of a peninsula formed by the sea and the Tagus, it is plain that if an army be posted across the peninsula, no enemy can penetrate into the city'without a direct attack on the army so posted. It was on this principle that the lines covering Lisbon were planned by Lord Wellington. Nature drew the rude outline of a strong defensive position, and art rendered it perfect. A tract of country thirty miles in extent from the mouth of the Zizandra on the ocean to Alhandra on the Tagus, was modelled into a field of battle; mountains were scarped perpendicularly, rivers dammed, and inundations formed; all roads favourable to the enemy were destroyed, and others made to facilitate the communications of the defenders; formidable works were erected to strengthen and support the weak parts, whilst numerous cannon, placed on inaccessible points, commanded the approaches and gave an equality of defence to the whole position.” These lines were not continuous and connected works; they consisted of independent forts, redoubts, flèches, redans, batteries, so placed as to command and enfilade every approach, and to support each other by a cross and flanking fire. The first line occupied a front of twenty-nine miles between the sea and the Tagus, and by means of telegraphs intelligence could be conveyed from one extremity to the other in a few minutes; whilst the troops, disposed in masses in the rear of the works, were ready to move upon any point of attack by interior communications shorter than any by which the enemy could advance. “The aim and scope of these works,” says Colonel Napier, “was to bar the passes, and to strengthen the fighting positions between them, without impeding the movements of the army. These objects were attained; and the loss of the first line would not have been injurious, save in reputation, because the retreat was secure upon the second and stronger line, and the guns of the first were all of inferior calibre mounted on common truck carriages, and consequently, immovable and useless to the enemy.” The two lines covered an extent of fifty miles, on which were erected one hundred and fifty forts, mounting in all about six hundred pieces of artillery.

Before this formidable position, defended by a double line of works, and by an army massed and ready to move upon any point by interior communications, the French remained five months, wasting their numbers and resources; until at length, finding it utterly impracticable to force any part of even the first line, they were obliged to retire from Portugal, closely followed and harassed by the army which they had previously driven out of Spain. Yet perfect as were the lines of Torres Vedras, and though one of the ablest of the French generals and a veteran French army were foiled before them, it is not meant to infer that the system of separate field-works is a model to be followed on all occasions; for, though the old method of covering a considerable front by a continued line of regular bastions and curtains has been generally condemned by modern engineers, there may be situations where the application of continued lines may be judiciously made. There is no fixed rule; the nature of the ground and of the position to be defended must determine the proper description of works.

But as in defence artillery should be combined with musketry, it is necessary that in the arrangement of lines provision should be made for the use of cannon; and as they should be preserved for action at the right moment, they should, when practicable, be mounted on carriages of such a height as will enable them to give their fire over a full parapet, the gun and carriage disappearing below the parapet after the fire is given, so that the loading may be effected in security. In particular cases, such as in flanks where the lateral range of the guns is restricted, and where the guns are not exposed, or are exposed to indirect fire only, openings in the parapet called “Embrasures” may be made use of, but they have many serious disadvantages :—they weaken the parapets; they offer distinct marks to the enemy; they are easily blown down by shells ; they are destroyed by the fire of their own guns; they are difficult to construct, and still more difficult to maintain. The interior opening, called the “Throat” of the embrasure is made wide enough to admit the muzzle of the gun, about 20 inches; the width of the outer opening called the “Mouth” is determined by the lateral range of the gun, which should not exceed 20°. The slope of the bottom of the embrasure, called the “Sole,” is determined by the object upon which the fire of the gun is to be directed. When required for indirect fire only, the sole is made countersloping; by this arrangement the exposure of the gun detachment is considerably lessened, and, in order to diminish still farther this exposure, the sides of the embrasures are made with a winding slope,—steep at the throat, from 6 to 1 or less, and flattening out at the mouth to 1 to 1. As a rule, embrasures should not be made till they are required, so that the parapet may be made solid in the first instance (see fig. 31).

The portion of parapet below the embrasure is called Genouillère (from genou, the knee), and should be 2 feet 5 inches high; the portion between two embrasures is called a Merlon, from the Italian merlone, a battlement; the bottom of the embrasure is calledits Sole; and, as has been suggested in respect to the superior slope of the parapet, it may be hori zontal for the first two feet from the neck, and then slope downwards as much as may be necessary for the depression required in firing. The direction of the embrasure depends on the direction of the line of fire: it may be either perpendicular to the crest or oblique. In the latter case, should the obliquity be very great, or exceeding 70°, the crest of the parapet must be made re-entering, so as to strengthen it near the neck, and to enable the gun-carriage to be brought up square to the parapet. The sides of the embrasure are called Cheeks, and should be revetted with sods, fascines, gabions (cylindrical baskets made of wicker, and filled with earth after they are in position), sandbags, planks, or hurdles. In fig. 32, on the left, at B, a direct embrasure is seen cut straight through the parapet; and on the right at A, an oblique one, both being intended to enfilade the ditches opposite them; and it will be observed that, from the obliquity of the right-hand embrasure, the interior of the work becomes so much exposed, that a traverse, T, behind the embrasure, becomes necessary. Barbettes are also shown in this figure—one at the salient at D for four guns, and another at C, perpendicular to the face, for two. The terrepleine of the Barbette should be 3¾ feet below the crest of the parapet; its length from front to rear from 18 feet to 20 feet; and its breadth, for a single gun, from 15 feet to 18 feet, according as it may be necessary to fire more or less obliquely; a breadth of 15 feet should be added for each additional gun. To add to the lateral sweep or range of the gun, without diminishing the banquette, or, in other words, the musketry fire, the barbette may be made wider in the rear than in front. In proportion to its magnitude should be the number of “Rampsssi or slopes of approach; as, for example, at C only one, at D three. The ramps should be from 8 to 9 feet wide, and their slopes should have bases equal to 4 times the height of the barbette. The lateral slopes of the barbette and of its ramps should be revetted whenever it is possible to obtain sods, fascines, hurdles, or other materials suited for the purpose, in order to economize space in the work, as the base of the slope may be then reduced to one-fourth or one-sixth the height; when unrevetted they have slopes of one-sixth. The terrepleine of the barbette may require, as at C, to be covered in flank by a traverse. The mode of constructing a barbette in a salient is exhibited in fig. 33.

At any point g of the face AB raise a perpendicular gh, either 18 or 20 feet in length, to include the amount of recoil; at the point h thus determined raise a perpendicular to gh, and prolong it to its intersection with the other face AC at E, then setting off AF on the other face equal to AE. On the capital AD set off a double perpendicular at any point i, prolonging it both ways, and making ik and il each at least equal to 4⅜ feet to represent the half breadth ®f the platform on which the gun-carriage is intended to stand and move; through the points k and I draw parallels to the capital, cutting the faces on the points m and n; join m, n, and parallel to the line mn draw the line OP at 18 or 20 feet distant from it, when wιnP0 forms the platform. Join FO and EP, and AEPOF will represent the contour or trace of the barbette. The manner in which the crest of the parapet is formed above the salient A, and the mode in which the firing may be effected in directions perpendicular to the faces, as well as in the direction of the capital, are shown in fig. 34.

In the case of a partly sunken parapet, in which the portion above the banquette is raised above and the portion below the banquette excavated below the plane of site,— as in fig. 35, the barbette constructed in the hollow portion will enable the gun to fire over the parapet; and it should be protected by forming a bonnetted embrasure, which may be sometimes made large enough, as here represented, to hold two guns. It need scarcely be added that an engineer ought to be ready to adapt any of the expedients here briefly noticed to the circumstances of the case before him, and that a mind stored with resources against any contingency is the highest endowment of a good officer. It must be obvious that in Field Fortification even a limited knowledge of the art of war opens a wide field for the exercise of the talents and resources of engineers; but the possession of a military coup-d’aeil, which comprehends at a glance the true bearing or character of objects and events is necessary for the conversion of stores of information to the best practical uses. In passing through a country, it requires an experienced eye to seize quickly on whatever it presents calculated to prove advantageous ordisadvantageous for attack or defence; to appreciate the value of villages, inclosures, and broken ground; to know where to dam up rivers, to scarp heights, to form abattis, trous-de-loup, and other obstacles; to select the best situations for field-forts and redoubts, and the best sites for batteries; and to arrange the defensive measures with reference to the number of troops disposable, so that the movements of the defenders may not be obstructed or retarded, and their communications may be short and easy. The variety of ground upon which military operations must be carried on precludes the possibility of laying down fixed rules in regard to this subject; the accidents of the ground, and the peculiar circumstances of each individual case, must determine the extent and description of the works to be constructed, as well as the obstacles most proper to be formed for retarding the advance of an enemy.

But though the observance of fixed rules be impracticable, general principles are of universal application; and certain maxims founded upon them hold good in the construction of field-works as much as in the erection of the complicated works of a fortress. These maxims, which are of invariable application, are—(1) that the works to be flanked must never be beyond the range of the projectiles used in the works flanking them, or, in other words, that the length of the lines of defence must never exceed the effective range of the weapons in use; (2) that the angles of defence must be about right angles; (3) that the salient angles of all works must be as obtuse as possible; (4) that the ditches must be efficiently flanked; (5) that the relief of the flanking works must be determined by the length of the lines of defence; and (6) that the works must be constructed with reference not only to the direct and immediate obstacles which they present to the enemy and to the positive effect of their fire on the approaches to them, but also to the support they derive from or afford to other works.

Field-works are either open at the gorge as in figs. 36, 37, 38, 39, or inclosed all round as in figs. 40, 41, 42, 43 They are of the following kinds :— [table]

[table]

The first class are of the simplest kind of field-works, and serve as cover in front of avenues, bridges (see fig. 49), causeways, and the like; being open at the gorge, they are only used when their extremities rest on rivers, or on obstacles which prevent their being turned, or when within the full sweeping fire of works in their rear. To increase the strength of a “Redan” its faces are sometimes broken into a kind of flank, as in fig. 36. In the “Double Redan,” or “queue d’hironde,” fig. 37, the re-entering faces defend each other, t, Tenailled Heads” (fig. 38) are used in situations which require a greater extent of front. “Bastioned Heads” (fig. 39) are also employed in similar circumstances.

“Redoubts” (fig. 40) are closed works of square or polygonal figure. In square redoubts provision should be made for defending the ground before the angles, which, however, are sometimes rounded or cut en crémaillère, so that a direct fire may be delivered from them.

Half-closed Redoubts, that is, redoubts in which the gorges are closed by thin parapets or timber stockades, may more fitly be classed here. They are employed when it is intended that their inter.or shall be open to artillery fire, so that an enemy having captured may not be able either to retain them or to convert them to his own uses.

Forts are works the parapets of which defend the ditches, and this distinguishes them from redoubts, the parapets of which do not.

“Star-Forts” (fig. 41) are designed to deliver a cross fire from the adjacent sides: but according to Jomini, they are the very worst description of fortification; they cannot have flanks, and the re-entering angles take so much from the interior space that it is impossible to place troops and artillery in them sufficient for their defence,” an opinion confirmed by the practice of Sir Richard Fletcher and Sir John Jones in the construe· tion of the lines of Torres Vedras, where the trace of the redoubts was varied to suit the conformation of the ground.

In “Bastioned Forts,” fig. 42, the flanking defence afforded by the parapets to the ditches is nearly perfect. As bastioned forts are only constructed in special cases of importance, no labour or expense should be spared in their formation. The bastioned face may be applied to any polygon provided that its angles are not less than 90°. When the angles are less than 90° the salients of the bastions are too acute.

“Demi-bastioned Forts” (fig. 43) inclose a greater interior space than Bastioned Forts, but a portion of their ditches are only defended by an oblique fire from the parapets of their faces.

The parapets of all these works should be of sufficient thickness to resist the fire of the heaviest guns that can be brought against them. In some cases it will be necessary that the parapets should be strong enough to resist the fire of light field-guns, whilst in others it will be sufficient if they serve as a cover to the men within them against musketry. This latter cover is that which, when time for more does not avail, is thrown up at the close of a march, after taking up a position, and which, if the army does not move next day, may be strengthened in parts, according to circumstances.

Continued Lines, or connected works, are resorted to in order to inclose the front of a position, or to connect important works or forts. The most simple trace is that of redans joined together by curtains (fig. 44); the ditches of these curtains can only be defended by an oblique fire from the faces of the redans, but this defect may be remedied by breaking the curtains so as to form nearly right angles with the faces of the redans, in which case they are called “Lines of Tenailles” (fig. 45).

“Lines en Crémaillère” have long faces, with flanks perpendicular to them, in order to defend their ditches

(fig. 46). When the faces can be directed towards ground upon which it is impracticable to establish enfilading batteries, this trace is good.

Bastioned Lines (fig. 47) form the strongest trace which can be given to continued lines, when the ground will admit of its adoption. A perfectly regular trace can only be applied to level ground. The ditches in field-works are often sloped en rampe towards the adjoining flanks, in order that the “déblai,” or quantity of earth excavated, may not exceed the “remblai,” or quantity in the mass of the rampart or parapet, a condition which might otherwise occur in field-works, where there is seldom any rampart, and only cover sufficient for the defenders.

Fig. 48 shows the general trace of “Lines with intervals.”

The salient works should never be beyond the range of musketry from the re-entering works, and the angles of defence between the two lines should be as nearly right angles as possible.

“Têtes-de-pont,” or Bridge-heads, are works, open at the gorge, whose flanks rest upon a river, designed to cover one or more bridges. The best situation for these works is the re-entering sinuosity of a river. As Tetes-de-pont (fig. 49) are usually constructed for the purpose of enabling a retiring army to cross a river in order, and to check an enemy pressing upon it, their trace and profile should be such as to secure this double advantage to the greatest extent possible. In Sir Howard Douglas’s able work on the Construction of Military Bridges will be found much valuable information upon this important subject.

The obstacles which are usually added to field-works, in order to render the approaches more difficult to the enemy, such as shelter trenches, entanglements, palisades, barriers, abattis, trous-de-loup, chevaux-de-frise, barrows, and crows’ feet, have been already described.

Defence of Open Towns and Villages (fig. 50).—To admit of a town being advantageously intrenched it is necessary that it should not be commanded within range of field-guns, that its houses should not be of a construction easily set on fire, such as of wood with thatched roofs, and that its extent should not be out of proportion to the means and time at the disposal of the defenders. The last consideration is of much importance and should be well weighed, as this kind of defence is prodigal of men. It is however rapidly organized; and, as the number and the nature of the troops allotted to it are effectually concealed, it is susceptible of being prolonged obstinately. When time presses the first step is to occupy the outer inclosures and to bar the principal thoroughfares upon the enemy’s side, to construct abattis and shelter trenches, to loophole the buildings flanking the barriers, and then to form a strong “shooting line” behind the outer inclosures, clearing enough of the ground in rear to receive the supports and reserves, and to enable them to act efficiently either in assisting to expel the enemy or in covering the retreat. The approaches to the “shooting line” should be cleared for a distance of at least 300 yards, by levelling houses, hedges, shrubberies, filling ditches, and clearing away whatever may favour the assailants. Wood should be cut down about 2 ft. 6 in. above the ground, and with wire or other means formed into an entanglement; hedges may often be so formed into most effective entanglements. The squares and open places should be occupied by the main reserves; the main approaches should be subjected to artillery fire; and distinct communications should be formed for the retreat of the defenders of the “shooting line.” The inclosure round the town should be completed, and for this purpose some houses should be removed, others should be loopholed, streets should be barricaded, secure places found for the magazines, and cover provided for the main supports and reserves, and wide and easy communications laterally and to the rear should be made. Streets leading out of town should be barricaded. The barricades should be sufficient to resist field artillery, and high enough not to be easily surmounted; and they ought to be flanked by loopholing the neighbouring houses. "When time presses, carts filled with dung with the wheels removed, sand-bags, bales of wool or cotton, and furniture taken from the neighbouring houses can be used as barricades. A church, a manufactory, a town-hall, a market, or any large substantial building should be converted into a keep, by blocking up useless entrances, loopholing its walls, and surrounding it by a ditch or abattis. Loopholes are slits or notches cut in walls with such tools as may be at hand. They are usually about 3 inches wide and 12 inches long externally, and are splayed internally so as to allow variation in the direction of the fire. Loopholes are cut vertically or horizontally as the case requires, and are much used as temporary means of supplementing the cover afforded by the parapets of temporary and permanent works; they are then formed of any materials at hand, such as sand-bags, logs of wood, and brushwood. Sandbag loopholes are the best, as the whole loophole is not necessarily destroyed by the blow of a projectile, and they are easily moved from place to place ; two sand-bags are placed side by side with an interval between them, and a third covers this interval. Logs of wood are disposed similarly; brushwood or board loopholes are embedded in the parapets. If a town is situated near a stream or river, by which part of it may be covered by inundations, the resources this affords should never be neglected.

Villages are intrenched on similar principles, and being generally surrounded by gardens with live hedges, the latter may be made use of in the lines of defence. If there should only be sufficient troops to defend part of a village or town, a part of it only should be intrenched, and should be separated from the rest by means of carts and barricades. If there are very few houses, it may be necessary to confine the defence to the church or churchyard. Villages are often in one long street; then only the rear portion is intrenched, clearing in front of this portion a space sufficient for the effective action of musketry.

The Destruction of Bridges.— Nothing is of greater consequence to a retreating army than to destroy the bridges in its rear, in order to retard the advance of the enemy. Its existence may depend upon the success with which this operation is performed. To destroy a stone bridge with gunpo⅝der a trench in the form of a cross is made in the crown of the arch, the branches of which are about 10 feet in length, and sunk to the top of the arch-stones. For an arch 3 feet thick, IGO ft of powder are placed in each trench; strong planks are then laid over the powder, and covered with rubbish. The fire is communicated by means of powder-hose or Bickford’s fuze. Stone bridges are destroyed also by simply cutting a trench about 18 inches deep across the crown of the arch, and placing in it 345 ft of powder covered,in the manner just described. This quantity has been found sufficient to destroy semicircular arches of 25 feet span, and of 3 feet in thickness at the key. Wooden bridges may be destroyed in various ways; they may be pulled to pieces, burned, or blown up. When there is time to take them to pieces, they are unspiked, and the timbers so separated that they may be speedily removed. The best method of burning such bridges is to tar them, and then to cover and surround them with fascines or tarred brushwood. Wooden bridges may be blown up by large charges of powder suspended under the superstructure, and fired in the manner above described. But these and other hasty demolitions may be more quickly and more certainly effected by the use of Compressed Gun-cotton, which is, weight for weight, four times as strong as gunpowder, and requires no tamping. Compressed gun-cotton is stored damp, and in this state it is perfectly safe for transport and handling, as it can only be detonated by the agency of a small quantity of dry gun-cotton, called a primer, and a detonator. The detonator is fired in the ordinary way or by electricity. Compressed gun-cotton is made in many convenient forms and sizes, such as 1 oz. and ⅜ oz. discs, 1 ft or 2 lb slabs, pellets, and grains. Generally it should be evenly distributed over the surface of stone bridges—if heaped, it forces an opening clean through. Supports of timber bridges may be destroyed by a girdle of half-ounce discs tied round them; or, if time avails, by charges placed in auger holes bored in them; ⅜ oz. of gun-cotton is sufficient for each square inch of the sectional area of the support. Iron bridges are destroyed by attacking the bottoms of the piers, or, in the case of girder bridges, the junction of 2 girders; 2 ft of compressed gun-cotton per foot lineal laid against an 18-inch brick wall will destroy it

A ford is rendered impassable by throwing large stones into it, by sinking boards with spikes standing upright in them, or by placing crows’ feet or harrows in it. A low rubble wall may be formed across it, so as not to be perceptible above - the water; strong stakes may be driven into the bottom, and trees fastened to them; waggons loaded with stones, with the wheels removed, may also be employed; and a number of other things which may often be found at hand will answer the purpose equally well. Rendering a ford impassable is only second in importance to the destruction of a bridge, when the enemy, whose progress it is desired to retard, either has no pontoon-train, or has outstripped it by the rapidity of his advance. By such expedients to retard the pursuit much valuable time may be gained by the retreating army.

The essential characteristic of all intrenchments which are formed of earth is that the musketry fire, on which the defence must mainly depend, being discharged over the crest of the parapet, the line of fire, will be nearly in the plane of the superior slope of the parapet, and perpendicular to the line of its crest; and hence opposite a salient angle, as in the Redan (fig. 51), there will be a large space of ground in this case extending over 180°- 60° = 120°, undefended by the fire of the work itself; this space is called a “dead angle.” Opposite re-entering angles, on the other hand, the defect is of a different kind, as the plane of the superior slope or plane of fire passing high above the foot of the escarp necessarily leaves it unseen and unprotected, notwithstanding that the two lines theoretically flank each other. The object, therefore, in arranging field works for mutual defence should be so to regulate their reliefs that the lines of defence should terminate at such distance from the ground as to give effective defence to the parts of the works intended to be flanked. The Redan may be considered the most simple form of defensive work, though a straight parapet terminating by short returns at each flank, in the form either of epaulements or of regular parapets, may occasionally be combined with defensive works. The redan is open in the rear, and the line joining B and C is called the gorge.

The “Lunette” is a redan to which flanks or lateral wings have been added; in form, therefore, it resembles a bastion. In fig. 48 Lunettes are shown so arranged that the faces of those in rear may flank the faces of those in front; but with respect to the distribution and arrangement of the works destined to form Lines of Intrenchment more will be said hereafter.

The “Tenaille” is the reverse of the redan; it consists of two lines forming a re-entering angle facing the exterior. It can, from its form, only be used in direct or approximate connection with other works which close up or cover the ends of its lines. Either alone or combined with redans it is very commonly used in continued Lines of Intrenchments. Fig. 44 represents a Line of Redans joined by straight lines, and fig. 45 a Line of Irregular Tenailles, whilst fig. 52 represents a normal line of Tenailles, of which the re-entering angles do not exceed 100 β , and the sides are equal, and fig. 53, an arrangement of Tenailles, with irregular sides, by which a Redan, as DEF, is interposed between every pair of Tenailles. The Line en crémaillère (fig. 46) is also derived from a combination of irregular tenailles, and is in many circumstances a very satisfactory arrangement. In selecting between these and other arrangements, including the bastion trace (fig. 47), the engineer must be guided by the nature of the ground and the special objects to be attained. A slight consideration is sufficient to show that the combination of regular tenailles in fig. 52 is only applicable to ground in itself regular. In most cases, however, the ground will be more or less irregular, and the works to defend it must be so also. When it is necessary to approach close to the bank of a river or a ravine, the Crémaillère Line (fig. 49) is the simplest and best, the short or flanking sides being so placed as to face the probable direction of approach, and next to that the combined Redan and Tenaille. Of open works, Lunettes admit of the most scientific arrangement, as they can be so placed in lines with intervals as reciprocally to flank each other, and thus to form a line of defence very similar to a regular bastioned line. The employment, however, of works open at the gorge must be restricted to positions where the enemy can only approach in front, his approach in other directions having been rendered impossible by obstacles or by other works. In every case it is desirable to take advantage of peculiarities in the features of the country, and to modify them into such obstacles as shall relieve the defenders from apprehension of danger, and leave them at liberty to direct their attention more exclusively to the weaker points of their position; but in no case should even apparently inaccessible points be left unwatched, as an enterprising and skilful adversary will at times surmount difficulties which had appeared insurmountable. As naturally defended points in a position can only be looked upon as exceptional advantages, it is evident that works left open at their gorges would be liable to surprise, and would therefore prove but imperfect instruments of defence. On this account it has been not unfrequently prescribed that such works should be left unclosed when within range of musketry fire from the defences behind them; but it is better to lay down the fixed principle that in all cases they should be closed at the gorge, as the power of driving an enemy out of the interior of such a work is of little value, for his object would be not to remain in its interior, but to turn its parapet to his own uses. The manner in which they are generally closed is shown in fig. 54, which is a lunette secured at its gorge by a loopholed stockade, an obstacle effective against an enemy, and, at the same time, easy of destruction, should he succeed in temporarily obtaining possession of the work. Any of the obstacles previously described, such as abattis, <fcc., may be used for the same purpose, but they have the disadvantage of not covering the defenders of the work from the enemy’s fire. An engineer in deciding between open works, such as have been described, and closed works such as will now be described, ought to take into consideration the circumstances of ground not only as affecting the security of the work itself, but as affecting the ease or difficulty with which support can at any moment be afforded to its garrison. Open works are not fitted for any position where they are likely to be left to their own resources, even for a short time, as small bodies of men cannot be expected to stand firm against a vigorous attack from a superior force, unless satisfied that support is at hand. Closed works, therefore, in which the parapet is continuous on all sides, can alone be relied upon under such circumstances; and the nature of the obstructions adopted in their construction should be such as to afford the garr⅛on a reasonable confidence that by a vigorous defence they may be able to hold the enemy at bay; for no general should expect to find in soldiers, as a body, that heroism which leads to self-sacrifice without hope. The easy capture of the the redoubts at Balaclava, garrisoned by the Turks, is an illustration of this principle; for though it is possible that they might have been longer maintained by French or British soldiers, it would have been unreasonable to expect that their defenders should remain firm until overpowered and cut down by their assailants, which must have been the result had not a supporting force been at hand to r> lieve them. The rules may therefore be laid down, that in all detached works the mode and time of relief should be palpable to the garrison; that the nature of the constructions should inspire the garrison with confidence in its power of resistance for a reasonable time; and, above all, that the garrisons of such works should be composed of the best soldiers.

Redoubts, as has been said, may be either regular or irregular polygons of any number of sides, but the square redoubt is the most simple (see fig. 40). All redoubts have the disadvantage of “dead” salient angles; and it is usual, therefore, to place the guns used in their defence in the salients, so that their fire may be along the capitals or lines bisecting the salient angles, as well as upon the dead space in front of them. The sides should be made to front the probable line of approach, and, as shown in one half of fig. 55, which represents ä Rectangular Redoubt, the escarp is sometimes sloped gently down to the bottom of the ditch, and covered with abattis or other obstacles, which can then be seen and defended in front by direct fire. It is indeed impossible to repeat too often that in all works the efficiency of defence must mainly depend on the power of arresting the progress of the assailants at those points which are under the fire of the defenders. The entrance to a redoubt should be made in the least exposed side, and be protected by a parapetted traverse placed behind it, as in fig. 55, where an arrangement of palisades is shown by which the traverse may be connected with the parapet of the works, and the entrance closed by gates or barriers. Traverses may be also constructed either for the purpose of defilade or for affording additional cover to the troops. They may be formed, when the work is sufficiently capacious, of long parallel epaulements, with a space be tween them, which can be covered over or blinded when it is likely that the work will be held for a considerable time, and when, in consequence, a more secure and comfortable lodging is desirable for the garrison. Magazines for ammunition may be constructed either against or in such traverses; and fig. 56 represents, in plan and section, a magazine behind a gabion traverse, and isolated from the parapet in front of it. This magazine is partly sunk in the ground, with sides of plank and a roof of strong timbers forming a ridge in the centre, covered first with fascines and then with 4 or 5 feet of earth. Its dimensions are— length 8 feet, breadth 5 feet, height 6 feet.

Having thus generally described this portion of the subject, it is necessary to determine the least size which can be given to redoubts, so as to ensure interior space sufficient to accommodate the garrison required for the defence of the parapet, remembering that in works not provided with flanking defences the whole parapet, unless secured in part by some insurmountable natural obstacle, must be defended.

A general formula may be easily obtained for determining the least regular polygonal trace in the following manner :—

Let X be the side in feet of any regular polygon, n the number of sides, A the interior surface reckoned from the foot of the banquette, y the number of men forming the garrison, f the number of linear feet allotted to each soldier, F the number of square feet occupied by each man in the interior,—then , nx A , n F x . fy =nx, and Fy=A, or 2∕=y=y î whence —j- =A. Again, let the perpendicular C⅛ from the centre of the polygon (fig. 57) to its side AB, be p, and let the distance db from the side AB to the boundary line of the available interior space mn be d; thenC5=j1-rf; andasOe: AB:: Cb: rnn,p:x: :p-d: mn, or mn≈ ——— = x-^~∙ Now, the value of p expressed as a function of x and of the angle of the centre φ, which is∙=x ⅜ cot. ⅜ φ, varies with the nature of the polygon; and replacing therefore the variable coefficient ⅛ cot. ⅜ φ by β, we have p=-βx, and mn, the side of the interior space mnpo, =χ--≈x-~=x- st-, and Cb = p βx β mn × ⅜ cot ⅞ φ — β (x - . The surface of the interior triangle Cmn = ⅛mn×Cb is thus = ⅞ β(x- , and A = γ (x-; whence also LstuL = Ist ( x - stX , and thence by reduction f * ∖ P ∕ X = -∣- j d + —+ l y∕7(2zz +y) í τhe τalues ofthe variable 0=⅛ cot. ⅞ φ are as follows:— [table]

Taking the square, and supposing we have <7=12 feet, ∕=3, F = 6×3 = 18, z = 62∙81 feet (21 yards), which may therefore be taken as the side of the smallest square redoubt to be defended by one rank only of soldiers, the garrison being 84 men in single rank, and a reserve equal to one-third of the garrison; if /— 2, then «=76*66 feet, or nearly 26 yards, the garrison being 156 men. If there are to be two ranks, ∕=1⅜, and x =89’6 = 30 yards nearly, the garrison being 240 men; and if two ranks, with a reserve equal to one-third of the whole garrison, ∕=1 and x=115 feet, or about 38 yards, the garrison being 456 men.

Triangular Redoubts are rarely used, as their interior space is small and out of proportion to the length of parapet: thus the smallest triangular redoubt to be defended by two ranks should have a side (x) 54 yards in length, and a garrison of 324 men, the total length of parapet required for this force being 162 yards; whereas a square redoubt of 38 yards side, which has a total length of parapet of only 152 yards, will accommodate a garrison of 456 men, admitting a “two-rank” defence, with a reserve of one-third the whole garrison. Another objection to Triangular Redoubts is the great amount of dead-angle space before the salients. Keeping these figures in recollection, the engineer will readily be able to determine his arrangement of the proposed garrison, and to limit himself to the least amount of work in parapet. If, however, he has to provide, in addition, for guns, for traverses, and for other constructions, he must increase the side of his square, bearing in mind that in the square of 38 yards side the augmentation of 1 yard per side adds only 12 men to the garrison, raising it to 468, whilst it adds 549 square feet to the interior space; so that, as the 12 men require only 216 square feet, there will be an addition of 333 square feet towards the additional provision specified. And if the side be increased to 45 yards, and the garrison to 540 men there will be a surplus interior space of 2709 square feet, being sufficient for barbettes, for three guns and one howitzer, and for a traverse; this size may therefore be assumed as the best for a normal redoubt. It has been usual to assume that a redoubt should not have more than 180 yards of parapet, but there does not seem to be any reason for this assumption; and it may be said with confidence that a redoubt with double this extent of parapet will be superior to a field fort of the same strength of garrison, even though the fort has the theoretical advantage of reciprocal defence. The ditches of larger redoubts are sometimes, when circumstances admit, defended by Caponnières (fig. 58) placed either at the angles or in the middle of the sides.

These caponnières are built of timber and roofed with logs or fascines, covered with earth; occasionally the ditches are defended by counterscarp galleries at the angles, constructed of the same materials as the caponnières, but buried in the counterscarp. Access is obtained by galleries revetted with timber descending from the interior of the work into the caponnière, and beneath the ditch to the counterscarp galleries. In fig. 40, one of the angles is shown with an indented parapet as a means of correcting the defect of a dead salient; but this is difficult of construction, and it will generally be preferable either to cut it off as in another angle of the figure, or to round it as in a third, or to occupy it by a gun en barbette, as in the fourth. Of Forts, fig. 41 exhibits a Star-Fort of eight points formed upon a square, which is far preferable to one of six points formed upon a triangle, as giving comparatively more available interior space. The defect, however, in this trace is that, though the intermediate angle F is sufficiently open—as it exceeds 60°—the angles A and B are less than 60°. Down to the lowest limit of such forts, in which AB of fig. 41 is taken at 60 yards, and the sides AE, EF, EBat 20 yards, there is still sufficient space to accommodate the necessary garrison, which should be in that case about 900 men. It is useless to describe those forms of star-forts which would not accommodate the required garrisons; but that represented in fig. 59 is well fitted for a large garrison. The following is a simple construction on a pentagon. Bisect AB in C; make the perpendicular CP = ⅜ AB; join APand BP; make Bd and Rd each ⅛ of AB, and join de, de. In this case the angles at A and B will be 64°, and the short sides (with an exterior side of 120 yards) each 23 yards. From what has been already said, Demi-bastioned Forts (fig. 43) will rarely be used; but when the proposed garrison requires a large amount of accommodation, and there is time to undertake such works, the bastioned trace should be adopted, as it introduces a principle not observed in the preceding traces, namely, that of defending the whole by a part, the opposite flanks EG, FG (fig. 42) of the two bastions GEAEG, GFBFG defending the intervening curtain GG between them, as well as the faces AE, BF of the bastions—whilst the fire of one flank necessarily sees the escarp of the opposite one and defends it. The bastions are indeed, like their analogous lunettes, works in themselves, the curtain being only a connecting line, forming several bastions into one connected whole. Fig. 42 is a square bastioned fort, but the pentagon is a better form, and should be adopted when practicable. The bastioned form of field forts has been derived from the more massive structures adopted in the permanent defences of fortresses, and its history, so interesting in itself, will be given in a future page. Little further need be said on this section of the subject, except to point out the great importance of field-works in securing a base of operations for an advancing army. Fig. 49 (page 435) exhibits, for example, a bridge head consisting of a bastioned front, with either simple straight branches or branches with a short flank, as shown in the figure (see also fig. 60 below). This is technically called a Horn Work; and if there had been two such fronts so placed as to throw a bastion in the centre, and connected as before with the river by straight branches, the work would have been called a Crown Work. Lunettes and even Redans may also be used, as in left side of fig. 36, for a similar purpose, where the object is first to secure the bridge from the enemy’s attack and fire, and secondly to allow the defending army to manoeuvre on the opposite side; but in proportion to the numbers to be passed over the bridge, and to the extent of advance contemplated, it will be necessary either to increase the importance of the works forming the bridge head, or to form more than one bridge in connexion with them. Nothing can be more fatal to a retreating army than to be driven back upon a river without a line of intrenchment sufficient to enable it to maintain its ground whilst its arrangements for passing the river are in progress. Fig. 60 exhibits one such arrangement, in which the Horn Work front has been much enlarged, and a lunette as a keep introduced within it. The mode in which the troops can move out at the sides, under protection of covering and flanking parapets, is shown, as well as the barbettes for guns, which become necessary in works having so important an object. Fig. 61 represents a line of Tenaille

Intrenchments in front of the lunette, and a line of intrenchment on the near side of the river, from part of which the last terminal branches of the tenailles are flanked. In this figure T, T represent traverses, and F, F either chains or lines of pickets placed across the stream,— the object of the first being to secure the bridge from the ricochet fire cf the enemy, and of the second to secure it from destruction by burning or explosive bodies launched by the enemy up the stream, to float down upon the bridge. More extended intrenchments might be formed of lines of lunettes with intervening intrenchments; but it is unnecessary here to pursue the subject further, as the engineer must necessarily adapt his works to the nature of the ground, and to the strength of the army for which he is required to prepare a defensive position, from which it may either advance or retire, without risk or confusion, as the necessities of war may require.

Permanent Fortification.

If, as has been stated, simple lines or works of fortifica-cation have been adopted even by the rudest tribes of wandering savages, for their temporary defence or security, the more massive and artistic works of permanent defence would seem to imply a certain amount of civilization. As an art, indeed, Fortification is almost co-existent with society. When men first assembled together for mutual protection, and placed their habitations in one spot, the law of necessity, springing in this case from the principle of self-defence, rendered it indispensable for them to adopt means for securing their families and their property against the sudden inroads of enemies. In the early ages, men were sufficiently protected by a wall, from behind which they could with safety discharge darts, arrows, and other missiles against an assailant. But when, in the progress of improvement, new and more powerful means of attack were discovered, it became necessary to increase, in a corresponding degree, the power of resistance; and so it came to pass that the feeble defensive structures of primitive times were superseded by solid ramparts, flanked and commanded by elevated towers; and, as the power of attacking fortresses or places of strength became augmented by sue cessive devices and inventions, so the means of resistance became proportionally increased, until the art of Fortification arrived at a state of comparative perfection, in which for many ages it remained nearly stationary.

The various improvements which were from time to time made, in strengthening the walls and in adding to the defences of ancient cities, are recorded in history, and need not be detailed in this place. The first walls of which we read were of brick. Amongst the ancient Greeks, brick and rubble stones intermixed were used, as we find from the description of the wall which connected Mount Hymettus with the city of Athens; but, surrounding several cities were works of Cyclopean character, built of huge stones, without mortar, placed -with their longer axis transversely to the line of wall, and arranged with great care and skill. The walls of Babylon and Nineveh indicate a prodigious advancement in the art of Fortification, and are justly accounted amongst the wonders of the ancient world. Those of the former city, ascribed by some to Belus, and by others to Semiramis, were thirty-two feet in thickness, and one hundred feet in height, surmounted at intervals by towers ten feet higher, and cemented by means of bitumen or asphaltum; they encompassed a vast area, and presented a solid defence, which no means of attack known in ancient times were sufficient to overcome or beat down. The walls of Jerusalem, though of smaller dimensions, appear to have been little inferior in strength and solidity to those of Babylon; for, in the siege of that capital by Vespasian, all the Roman battering-rams and other engines, though used with the utmost vigour through a whole night, only succeeded in disengaging four stones in the masonry of the tower of Antonia. But after Fortification had arrived at the state in which we find it in the works of these and other cities, it remained stationary for ages, and perhaps even retrograded somewhat, until the discovery of gunpowder, the invention of artillery, and the application of both to military purposes, effected an entire revolution in the principles of attack and defence. Then the towers, which had formed secure flanking defences against assailants armed only with arrows and darts, no longer afforded protection against projectiles discharged from cannon; and even those battlements which had defied the catapult and the battering-ram speedily fell before the new force with which they were assailed, burying their defenders in their ruins.

The ancient system of Fortification being thus found of little avail against the new method of attack which came into general use towards the close of the fifteenth century, it became indispensably necessary to adopt improved methods of defence. The plan of fortifying with bastions is believed to have originated with the Italians early in the fifteenth century; though Papacino D’Antoni, professor of artillery and engineering of Turin, states, in Architettura Militare (1759), that several small bastions had been constructed in the preceding century, and that the ruin of a large bastion which had formed part of the fortifications of Turin, built for Duke Louis of Savoy, still existed in the royal gardens at that time. The bastions on the enceinte of Verona, built by the Italian engineer Micheli, in the year 1523, are generally supposed to be the oldest extant; and the next, probably, are those of the citadel of Antwerp, which were constructed for the emperor Charles V. in 1545, by the Italian engineer Paciotto D’Urbino. These bastions are small, with narrow gorges and short flanks and faces, and are placed at great distances from one another, it being the invariable practice, at the time when they were built, and for a considerable time afterwards, to attack the curtains, and not the faces of the bastions.

Errard of Bois-le-duc was the first in France who laid down rules respecting the best method of fortifying a place, so as to cover its flank. He was one of the principal officers of the engineers in ordinary to the king, a corps formed by Sully, who was grand master or master general of artillery in the reign of Henry IV., out of the best instructed and most experienced military men. This corps is now the Corps de Génie, and to this day maintains its scientific character. At the command of the minister, Errard wrote a book on the subject, which was published in 1594, and in which the details of his method are explained. As a writer on fortification, he was preceded in France by Beril de la Treille, who published his work on fortifying towns and castles in 1557. Errard fortified inwards; and in the square, pentagon, hexagon, heptagon, and octagon he made the flank perpendicular to the face of the bastion; but in the enneagon, and in polygons of a greater number of sides, he made it perpendicular to the curtain. In his method, however, the gorges are too small, the embrasures are too oblique, and the ditch is almost defenceless. This engineer constructed part of the enceinte of the citadel of Doutens, the citadel of Amiens, and some works at Montreuil and Calais.

Antoine de Ville, who succeeded Errard, published a treatise, dated 1629, in which he completed much that his predecessor had only sketched, and rectified various defects in the method of the latter. He was employed under Louis XIII., and constructed new enceintes for Montreuil and Calais. His method of fortifying has been denominated by some the French Method, and by others the Compound System (Système à trait compose), because it united the Italian and Spanish methods, from the latter of which it differs only in having no second flanks and fichant lines of defence, and in not confining the flanked or salient angle of the bastion to ninety degrees. The leading maxims of De Ville were to place the flanks perpendicularly to the curtain, to make them equal to the demigorges, or a sixth part of the side of the interior polygon, and, in the hexagon and all higher polygons, to confine the flanked angle to ninety degrees. But this method is liable to nearly the same objections as that of Errard, as the embrasures are too oblique, especially in the polygons, and the ditch is ill defended.

In 1645, sixteen years after the publication of De Ville’s, appeared the treatise of the Comte de Pagan, which contained the development of a system that, in a short time, entirely superseded those of his predecessors. It was the Comte de Pagan who first disengaged the science of Fortification from a number of suppositions which custom had consecrated, and which, resting more on abstract mathematical reasoning than on practical experience, had hitherto retarded the progress of the art. This engineer served at twenty-five sieges with great reputation; but having become blind at the age of thirty-eight, he was obliged to retire from the service, in which he had already obtained the rank (then second only to that of marshal of France) of mareschal-de-camp, and he died six years after completing the treatise above mentioned. He had from his earliest years devoted himself to the study of mathematics and fortifications, and he published several works on astronomy besides his celebrated work on Fortification, Pagan made the flank perpendicular to the line of defence, in order as much as possible to cover the face of the opposite bastion; and he devised a method of building casemates peculiar to himself. Vauban borrowed from Pagan the length of his perpendicular, and Allain Manesson Mallet, whose construction has found much favour, proceeded upon the principles Pagan had laid down.

The Mareschal de Vauban was born in 1633; and at the time of the Comte de Pagan’s death, he had already acquired reputation at several sieges. Vauban followed up the principles suggested by Pagan, and employed them extensively, with consummate skill and judgment. He constructed 33 new fortresses, repaired and improved 100, and conducted about 50 sieges. His extensive works, especially the treatise De V Attaque et de la Défense des Places, published in 1737, speak for themselves. From these works have been compiled the systems which, in the military schools, are denominated Vaubau’s first, second, and third systems of Fortification, and which the reader will find developed in the sequel. Had the genius of Vauban been applied to the discovery of a method for securing a permanent superiority to the defence of fortified places, posterity would have been greatly indebted to him, and even humanity would have had cause to rejoice in such a triumph of military art. But, being engaged in the service of the most ambitious monarch of modern times, Louis XIV., he applied his great talents to forward his master’s views, and perfected that irresistible system of attack which has ever since been so successfully followed. Before his time the superiority was on the side of the defence; but he so completely reversed the case that the success of an attack, conducted scientifically and with adequate means, has been until the present time a matter of certainty. Vauban was no ordinary man in any sense. As the inventor of parallels in sieges, and of ricochet fire, he stands in the first rank of military engineers; and as he conducted 53 sieges, and took part in 140 battles and skirmishes, it must be admitted that in respect of experience he stands in no inferior position. At fifty-five years of age he attained the highest honour of the French army, being created marshal of France; yet amidst his stirring and successful military life he never ceased to turn to account the geometrical knowledge for which he was distinguished when a youth, and which had obtained for him the early notice of the Prince de Condé. His mind was never idle, and was constantly directed to projects of public utility, civil as well as military; and he left behind him records of such labours in 12 folio manuscript volumes, entitled Mes Oisivetés, a wonderful monument of his ability and industry.

Μ. Minno, Baron de Coehorn, first a general of artillery, then a lieutenant-general of infantry, and ultimately direc∙

tor-general of all the fortified places belonging to the United Provinces of Holland, was the contemporary and rival of Vauban. This able engineer, convinced that, however expensively the rampart of a town may be constructed, it cannot long resist the shock of heavy ordnance, invented three different systems by which such obstacles are thrown in the way of a besieging force that, although the place be not thereby rendered impregnable, it can only be reached with great difficulty and hazard. But these systems, without modification, are only applicable to low and swampy situations, such as are to be found in Holland, and are therefore not available in localities of a different description. Nevertheless, Bergen-op-Zoom, Mannheim, and other places fortified by this engineer, particularly the two named, have very great merit, inasmuch as it is impossible for a besieger to penetrate into any of the works without being exposed, on all sides, to the fire of the besieged, who are under cover, and from whose artillery and musketry fire it is scarcely possible for an assailant to shelter himself. In fact, Coehorn was a great master, and combined with the bastioned trace, as will be explained when his system is noticed, many of the means of defence springing from another source. He published his first work on Fortification before he had acquired much experience; and in fortifying Bergen-op-Zoom, which is allowed to be his masterpiece, he did not reproduce, except in fragmentary details, any of his published systems.

Since Vauban’s time several improvements have been suggested, particularly by Cormontaigne, who entered the corps of French engineers in 1716, nine years after Vauban’s death, and died a mareschal-de-camp in 1750. Some account of the system of Cormontaigne will be found in a subsequent part of this article. The three methods enunciated by Belidor are all applicable to an octagon of 200 toises. Scheiter distinguished his systems as great, mean, and little, in imitation of Pagan, requiring the exterior sides of the polygon to be 200, 180, and 160 toises respectively. He adopted from Castriotto detached bastions, and made use of a continuous fausse-braye. Fritach, a Pole, proposed two methods, which he exemplified on different polygons. Dogen, a Dutchman, after enumerating, in a large volume on Fortification, various modes employed by different writers for determining the salient angle, selected three as most worthy of approval, and proposed as many methods of construction, one of which is borrowed from Fritach, the Pole. Pietro Sardi, an Italian, suggested a peculiar method of construction on a hexagon. The Sieur de Fontaine found the flanked or salient angle of the bastion by adding 15’ to half the angle of the figure, from the square up to the dodecagon, in which last it becomes 90°, and at this he continued it in all the higher polygons. He also constructed outwards, and, in every regular figure, made the curtain equal to 72 toises, the face of the bastion to 48, and the flank, which he placed perpendicularly to the curtain, to 18 toises, or a fourth part of the curtain. 0zanam and Müller delivered each four methods of construction, the particulars of which will be found in their respective works. In 1751 Charles Bisset, who, as engineer-extraordinary, served with the duke of Cumberland in the Netherlands, and was present during the siege of Bergen-op-Zoom by Marshal Lowendahl, published a treatise on the theory and construction of Fortification, in which there are many sensible and judicious remarks; and this may also be said of an Essai sur la Fortification, ou Examen des Causes de la grande supériorité de Γ Attaque sur la Defense, published anonymously in 1755. In a work entitled Science de la Guerre, which appeared at Turin in 1747, a new method of construction is proposed, in which the principal novelties are mines under all the works, and regular communications with them by means of subterraneous galleries, to be resorted to as the enemy approaches the body of the place. The third volume of the Oeuvres Militaires contains useful observations and maxims relative to irregular Fortification; andin the supplement to the Reveries of Marshal Saxe, by Baron d’Espagnac, the subject of Fortification is amply discussed, and an accurate description given of the different means of attack and defence. Besides the writers above enumerated may be mentioned the Chevalier St Julien, an able engineer, who published a method by which, he asserts, works may be constructed at less expense, yet in such a manner as to render the defence more formidable; Francisco Marchi, of Bologna, who in 1599 furnished no less than 139 different methods of constructing fortifications, many of which are valuable, and from which subsequent engineers have greatly profited; Bombelle, who established three kinds of Fortification, called the grand royal (grand royal), the mean royal (moyen royal), and the little royal (petit royal)·, Blondel, who published a system divided into two principal heads, the great and the little, whose exterior sides are respectively 200and 170toises; Donato Rosetti, a canon of Leghorn, who wrote on the method of constructing works in what he calls Fortification à rebours, or Fortification in reverse, so denominated because the re-entering angle of the counterscarp being opposite to the flanked angle, it will, according to him, be necessary to attack it from the reverse side of the other works; and Antonio de Herbart, major of artillery in the duke of Würtemberg’s service, who published a treatise on Fortifications with what he calls angular polygons. The treatise entitled Nouvelle Manière de fortifier les Places, tirée des méthodes du Chevalier de Ville, du Comte de Pagan, et de Μ. Vauban, avec des Remarques sur Γordre renforcé, sur les desseins du Capitaine Marchi, et sur ceux de Μ. Blondel, which appeared in 1689, is full of strong reasoning, whence the author deduced a new system; but it contains little that is original, though it gives numerous references to what had previously appeared, and disposes the different parts in a judicious manner. Μ. de Montalembert’s system of casemated and reverse fire has been in part adopted in the splendid fortress of Alessandria, in Italy, which was constructed under the direction of Napoleon.

Of the more recent treatises on fortification, that of Μ. de Bousmard, entitled Essai General de Fortification, d’At- taque et d.e Défense des Places, dans lequel ces deux Sciences sont expliquées et mises l’une par Γ autre à la portée de tout le monde, is very elaborate and complete, and enjoys a deservedly high reputation for accuracy and research.

Carnot’s Traité de la Defense des Places Fortes was written to serve a temporary purpose; and the exaggerated celebrity which it acquired on its first appearance has been succeeded by an equally unfounded neglect. The more prominent innovations recommended in this treatise were— first, an alteration, which, however, was not original, in the trace or outline of the polygon; secondly, the suppression of the exterior revetment of the covered-way, known as the counterscarp; thirdly, the detachment of the escarp-wall from the rampart, and the construction of the latter without revêtement; fourthly, destructive personal conflict with the besiegers by means of frequent sorties; and, lastly, vertical fire as the basis rather than the accessory of the defence. With regard to these innovations, all of which the reader will find ably discussed in Jones’s Journals of Sieges in Spain and Portugal, vol ii., it may be remarked that by means of an increased expenditure for retrenchments and casemates, as recommended by Carnot, the strength of particular portions of the polygon may be increased; and that, if he has failed in tracing a perfect front, founded on the basis of Montalembert’s system of casemated and reverse fire, he has at least rescued a valuable suggestion from unmerited neglect, and rendered an important service to science by directing the attention of military men to means likely to create a barrier against the growing powers of the attack.

The Traité de Fortification Souterraine, suivi de quatre Mémoires sur les Mines, by Μ. Mouzé, lieutenant-colonel of engineers in the French service, published at Paris in 1804, is the most complete work on the subject of which it treats which has yet been given to the public. Subterranean Fortification is a branch of the art which, until recently, was wholly neglected in England, and in which British engineers were far behind their brethren of the Continent. We learn from Colonel Jones’s work on the Peninsular sieges that the duke of Wellington’s army in Spain was without a trained sapper or miner until late in the year 1813. In this respect things are now changed, and in the Engineers the army has the assistance of a body of men well instructed in the duties of the trench, the sap, and the mine, though it cannot be said even now that the corps of Engineers is of sufficient strength. Nor can this corps, as some contend, be supplemented by civil labour in time of war. Discipline is the foundation upon which the whole military system rests, and the highest skill, unless strictly subordinated to it, will avail little in war. The undisciplined labourer, who, under ordinary circumstances would have worked with the greatest effort, would be found worse than useless if forced to work on his knees in a sap, exposed to an enemy’s fire, or upon his back in a countermine, with the knowledge that the enemy’s miner, though he cannot fix his precise position, is probably within striking distance.

Before going further it is desirable to recur to the earlier methods, and to investigate the manner in which the ancient arrangement of a wall, with round or square towers, passed into the present systems of defence. Fig. 62 will explain the natural and probable manner in which the old tower or rather tower-fort (baluardo) grew' into the pentagonal bastion. If, for example, lines of defence be drawn from the extremes of two adjacent curtains to the angles a and c of the square tower-fort A, a space would be left, cba, unseen from the adjacent forts B and C, and therefore undefended, except by downward or vertical fire from machicoulis, or projections from the walls supported by corbels made for the purpose. Such a space would be turned to account by the besiegers in fixing their scaling ladders; and the change of the straight line ac into the two faces cb, ab seems but the result of a self-evident necessity. As the work became enlarged, the portions of the fort within the connecting walls m, m were omitted, and the flanks de, fa alone remained of the old wall, forming with the faces the bastion fabed, which only required to be improved in proportions to become the bastion of modern times. It is, however, said that the towers were sometimes placed with an angle salient as in B, and if so, omitting the portions nn, the resulting bastion has a strong analogy to those of Errard before mentioned. By using the old wall merely as a retaining wall, and as an obstacle against escalade, and adding to it a rampart and a parapet of earth, the Italians completed the system of bastioned defence, which, notwithstanding all the modifications of the French, ought to be called the Italian system. In this system, whilst imitating the construction of the old towers by using casemated or masonry-vaulted chambers for artillery, in addition to the guns mounted on the rampart, the Italians placed the musketeers on the banquette of the parapet, and made them fire over it. Now this arrangement of the musketry fire is an essential characteristic of the Italian system, and the reliefs of the several works are by it restricted within certain limits, as it is necessary so to determine the levels of the opposite flanks that the fire along their superior slopes shall defend the whole of the intervening curtain: but there are other modes of using musketry as well as artillery fire in the defence of the ditches, and on these were founded other systems of Fortification.

The first Italian writer on Fortification was Tartaglia, whose work was published in 1546; but the really first writer on the science was Albrecht Dürer, a great painter, sculptor, and engraver, and a civil and military architect, whose work is dated 1527, being published one year before his death. This remarkable man founded his system on the old circular tower-forts C, fig. 62, with wdιich the dead space is much less than with square tower forts, and, enlarging the towers to an enormous extent, he adopted the name “Bastei,” or in the plural “Basteien,” for his new work. As attention was at this early period more directed to cannon than to the rude musket as an instrument of defence, it was natural that the latter should be less considered in these arrangements than the former. Dürer based his systems on the principle tlιat the defences of basteien or other works which depend only on the cannon placed on their terrepleines may be effective whilst the enemy is at a distance, but cannot be so when, under cover of his epaulements, he has reached the ditch; and leaving therefore to the cannon on the terrepleine the task of firing upon the enemy’s troops and batteries at a distance, he placed cannon and musketry either in vaulted galleries running along the base of the escarp, or in caponnières, also vaulted or casemated works, built across or transversely to the ditch. The great circular bαstei of his third and most improved system was no less than 130 yards in diameter, with an escarp 120 seet high, a ditch in front 100 feet wide, and a massive envelope, about 80 feet thick and 100 feet high, formed of earth with thick masonry revêtements both in front and in rear, as a mask between the main work and the counterscarp. Such gigantic proportions as these have led many to consider Dürer as little more than a speculative writer, but this would be an unjust estimate of his real merits. Reducing his works to more reasonable dimensions, they would, with proper modifications, have become practicable, and they have afforded many useful hints to the scientific engineer. The defects of the circular form were compensated by the grazing fire of the caponnières in his system, and the main work was retained in an effective state by the cover afforded to it by the envelope. We shall have occasion to refer again to Dürer, but in the meantime it may be said that whilst the Italians are properly considered the originators of bastioned systems with an earthen parapet over which the musketry fire is directed, Dürer has an undoubted claim to be considered the author of the systems of Fortification in which casemated defence in the main works and in the caponnières becomes the essential characteristic—a system which has proved more fertile in results in modern times than the bastioned system.

Systems of Permanent Fortification.

1. Vauban ’ s First System.

Before commencing to draw a plan of Fortification, it is usual to determine the polygon on which to describe it. In Plate III., fig. 1, the angle taken is that of an octagon, and the length of the side is 360 yards. In constructing a fortification, a figure is determined on, as near a regular polygon as possible, within which the enceinte or chain of main works is to be contained. The enceinte or body of the place consists of as many bastions, connected with curtains, as there are sides to the figure, and each of these is made about 400 yards.

The Principal Line or Outline denotes the line by which the figure of the work is defined. This line is supposed to pass along the cordon of the escarp, and is that from which all the other parts of the work are set off.

The Exterior Side, or side of the polygon above mentioned as equal to 360 yards, is that upon which the Front of the Fortification is described, and it extends from the flanked angle of one bastion to the corresponding flanked angle of the next, as AB. These lines are bisected, and a perpendicular CD is drawn from the point of bisection towards the place, its length being proportional to the length of the exterior side and adjacent angle of the polygon,—that is, one-sixth for the hexagon and all figures of a greater number of sides, one-seventh for the pentagon, and one-eighth for the square.

The Lines of Defence, AEG, BFH, are drawn from the extremities of the exterior sides through the point D, and produced to an indefinite length; and upon the lines so drawn are set off two-sevenths of the exterior sides, equal to 102¾ yards, which mark the points for the shoulders of the bastions, E and F. The distance between these points is then laid along the continuation of each line of defence, viz., from E to G and from F to H, and the line connecting G and H is the curtain GH, from the extremities of which lines are drawn to the points marked off for the shoulders of the bastions, and these form the flanks. In this manner is drawn a Front of Fortification, and this being repeated upon each side of the polygon, completes the works of the enceinte, or body of the place.

Vauban divided his first system into three classes, namely, the little, the mean or intermediate, and the great. The first he used for small forts of four or five sides, citadels, horn-works, and crown-works, making the exterior side from 120 to 240 yards, the perpendicular equal in the square to one-eighth, and in the pentagon to one-seventh, and the faces of the bastions in each equal to two-sevenths, of the exterior side. In the mean or intermediate, which is adapted for all sizes of towns, the exterior side varies from 250 to 360 yards, the perpendicular is one-sixth, and the faces of the bastions are two-sevenths. In the great the exterior side varies from 360 to 520 yards. This was never adopted for all the sides of a place, but only in the case of one which happened to be near a river or a marsh, when the distances of the bastions should be so regulated that they may not be out of musketry range from one another. When the curtain becomes unavoidably too long, this defect is in part remedied by erecting on it a flat bastion, which is not so high as the rest of the works.

Ground which will admit of being regularly fortified throughout is seldom met with; nevertheless, the rules of regular fortification must be observed as nearly as possible. These are—that the flanked angles should not be less than 60°, that the lines of defence should not exceed musketry range, and that the sides should be lengthened or shortened so as to obtain a well-proportioned front upon each. After an irregular place has been reduced to as regular a figure as possible, lines are drawn parallel to the sides of the figure at the distance of about 50 yards from the houses, in order to give sufficient space for the rampart; and these lines form the interior polygon, which may be fortified outwards, by setting off the demigorges of the bastions, and raising their flanks at angles of 100° with the curtain. Or the exterior side may be formed and fortified inWards by drawing a line parallel to each of the interior sides; and when the angle is that of a polygon of more than five sides, the distance from the exterior to the interior sides should not be less than 100 yards. If a side extend from 360 to 520 yards, the perpendicular should be diminished to about 50 yards, and the faces of the bastions be made from 100 to 120 yards. All these dimensions should, however, be now much increased, and placed in relation to the range of the modern rifled small arm.

The Ditch or Fosse is an excavation of from 15 to 30 feet in depth, and from 30 to 50 yards in breadth, surrounding the rampart on the exterior side; the earth dug out of it serves for the rampart and parapet. The side of the ditch next the place is called the escarp, the side next the country is called the counterscarp, and is made circular opposite the salient angles of the works. In the figure arcs are described with a radius of 30 yards, opposite the salient angles of the bastions, tangents to which are drawn upon the shoulders of the neighbouring bastions, and thus the width of the ditch is fixed. The general dimensions of a ditch should be such that its excavation, or déblai, would produce sufficient earth, or remblai, for the formation of the works. The breadth varies from 30 to 50 yards, in order that, in passing across it to the assault, the enemy may, for a considerable time, be exposed to the fire of the works; and its depth must be such as to render difficult the escalade of the parapet, as well as to prevent the besiegers at the crest of the glacis from being able to see the lower part of the revetment of the escarp. The line of the counterscarp is drawn from the rounding at the salient angles of the bastions upon the shoulders of the bastions next adjoining, in order that the whole of the ditch may be defended by the fire of the flanks of the bastions. Ditches are of three kinds,—wet, dry, and such as may be rendered either wet or dry. The wet ditch is effectual against surprises or sudden assaults, excepting during hard frost, for it may be passed when frozen, as in the attempt to surprise Bergen-op-Zoom in the year 1814; but thenumberof bridges of communication, which require continual repair, and the difficulty of making sorties, render a wet ditch extremely inconvenient. A dry ditch, which is capable of containing works for its own defence, and by means of which communications round the works may more easily be maintained, is therefore preferable; but the third kind, which unites the advantages of the other two, is to be preferred to either. It is only in particular situations, however, that such a ditch is practicable.

The Tenaille, in the form given to it by Vauban, does not appear in the works of earlier engineers, but it seems to be naturally derived from the trace of Rimpler (1673), in which the middle flank is analogous in function to the tenaille, and occupies its position. It is a work placed in front of the curtain, and is thus formed :—its side faces are upon the lines of defence, and commence at points 11 yards distant from the shoulders of the bastion; its front face is 28 yards from and parallel to the curtain; its gorge is parallel to and 17 yards from the faces; its ends are parallel to the flanks of the bastions. The relief or height of the tenaille is determined by that of the neighbouring flanks, and it has a parapet of 7¾ feet in height and from 12 to 15 feet in thickness. The use of the tenaille is to cover the postern gate, which is often made in the curtain or flank; in dry ditches it protects the troops formed behind it for the defence of the ditch; in wet ditches it covers the boats collected for the same purpose. It adds materially to the defence, as its fire, from being more horizontal and nearer to the bottom of the ditch, is of course very effective. It fires into the ravelin, and acts as a partial traverse to the escarps of the curtain and the flanks.

The Ravelin or Demilune was originally designed to cover the entrance to the fortress, but it soon developed into a most important work of defence, appearing as such in some early Italian Traces. Speckle, the great German engineer, who fortified Schlottstadt, Hagenau, Ulm, Colmar, Basel, and Strasburg, was, however, the first who recognized fully its importance, and laid down the rule that “great ravelins materially augment the defensive power of a bastioned system.” Constructed upon this principle, the ravelins of Speckle were even larger than the ravelins of Cormontaigne’s system, and covered nearly the whole of the bastions, their faces being directed on the salients of the bastions and their capitals, extending about 150 yards in advance of the exterior side of the polygon. Speckle was a man of science, having studied mathematics and military engineering in his youth, and perfected his knowledge by visiting and inspecting the most remarkable Italian Fortifications existing in his time. The Ravelin is a work constructed opposite the curtain, of two faces meeting in an outward or salifent angle, with two demigorges formed by the counterscarp. Its use is to cover the curtain, the gates, and the flanks of the bastion. The Ravelin is constructed as follows. At 11 yards from the shoulder along the faces of the bastion, points are set off; an arc is described from the angle of the flank upon the perpendicular produced, with a radius of 160 yards; from this intersection lines are drawn towards the points set off, but not further than the lines of the counterscarp; at the intersection of the lines of the counterscarp or re-entering angle 6 yards are set off on the capital or line bisecting its angle, whence lines are drawn parallel to the lines of defence till they meet those of the counterscarp. Stairs, called pas-de-souris, are constructed here in order to facilitate the entrance into the ravelin from the ditch. The ditch in the ravelin, which is 24 yards in breadth, is made circular at the salient angle, and drawn parallel to the faces till it joins the main ditch.

The Covered-way was first described by Tartaglia in 1554, so that it must have been used at a very early epoch of Italian Fortification. Some of the first bastioned fortresses were, however, without this highly important work; and it is recorded that at the siege of Vienna by the Turks, the garrison having made a sortie, some companies were pursued by the Turks up to the counterscarp, and forced over it into the ditch. The necessity of being able to assemble under cover from the enemy’s fire the troops intended for a sortie, and to afford them when repulsed a place for reforming and checking the enemy’s progress, and thus insuring an orderly retreat into the body of the place, soon became apparent, and a Covered-way was supplied to works originally constructed without one. It is a space of 10 yards in breadth, extending all round the work between the edge of the counterscarp of the ditch and the parapet which covers it; this parapet is from 7 to 9 feet in height, and has a banquette for musketry. The superior part of this parapet forms a gentle slope towards the country, which terminates at the distance of from 40 to 70 yards; and this slope is called the Glacis. The Covered-way serves for drawing up troops in order to make sorties, and costs less than any other part of the works in proportion to the difficulty of taking it. In its salient and re-entering angles are open spaces called Places of arms.

The Salient Places of arms are the open spaces between the circular parts of the counterscarp and the prolongation to intersection of the branches of the covered-way. The Re-entering Places of arms are constructed with two faces, forming a salient angle of 100° with the covered-way. The demigorges of the re-entering places of arms are generally from 24 to 30 yards; but when they are intended to contain a redoubt or intrenchment, they are from 40 to 48 yards. The Re-entering Places of arms are meant to flank the branches of the covered-way, and to contain the troops for its defence. The Salient Places of arms also serve for the assembly of troops for the defence of the covered-way.

Traverses are constructed across the covered-way, upon the prolongation of the sides of the ravelins and bastions, perpendicular to the line of the counterscarp; they are from 18 to 20 feet thick, and serve to cover the troops from the enfilading fire of the enemy. Other traverses are constructed between these, so placed that the distances between them should not exceed 40 yards. Passages 10 or 12 feet wide, which are formed by cutting into the parapet of the covered-way round the ends of the traverses, afford thorough communication; the openings are closed when necessary by gates. In the more improved systems of Cormontaigne and others, these openings are constructed in such a manner that each can be defended by the fire from the traverse in rear of it.

The Glacis, as already stated, forms a gentle slope from the parapet of the covered-way towards the country, and varies from 40 to 70 yards in length. Its parapet cannot be ruined by the fire of the enemy; it covers the revetment of the body of the place; and being an inclined plane, it can be easily seen and defended from any part of the works.

The Rampart is an embankment of earth, and is the part of the works next to the town which it surrounds. It must be broad enough to carry the parapet and to provide sufficient space behind it for working the guns, and for the free passage of the defenders. The Ditch is immediately in front of the rampart, which is sustained by a revetment-wall of masonry or brickwork, called the escarp, strengthened by interior buttresses, called counterforts, placed at intervals regulated by the height of the wall and their own thickness. The Rampart is divided into the terrepleine, the banquette, the parapet, and the escarp. See Plate HL, fig. 4.

The Revetment or face of masonry around the work on both sides of the ditch is intended to prevent the earth above from falling into the ditch. To ascertain the proper thickness of masonry for revetments has always been a matter of considerable trouble and difficulty. General Sir Charles Pasley of the Royal Engineers has given the following rules. (1) For full-scarped revetments without berms, and for demi-revetments having berms equal to one-fourth the height of the masonry, the thickness of the wall should be seventeen-sixtieths, and the length of the counterforts or buttresses one-fifth of their height. (2) For demi-revetments without berms, the mean thickness of the wall should be three-tenths, and the length of the counterfort one-fifth of the height. (3) For counterscarp revetments, having only to retain simple terrepleines, the mean thickness should be one-fourth, and the counterfort one-sixth of the height. In all these cases General Pasley supposes the revetment to be countersloped, that is, to have the exterior slope in a vertical plane, and the interior face inclined, so that the base of the wall may be broader than its top by one-fifth of its height; and he also supposes the counterforts to be rectangular, and the intervals between their centres to be equal to four times their width. (4) He recommends that the foundations be made deeper in rear than in front,—that the courses of masonry form an angle with the horizon of about 10° till within a foot from the exterior, where they should be horizontal, to prevent the rain from penetrating,—and that the interior face of the wall should be of irregular form. The lateral pressure of the earth against the revetments may be diminished by building arches in one or two tiers between the counterforts.

The Cordon is a round projection of stone, about a foot in diameter, near the top of the revetment wall, which serves to throw the drip of rain off the face of the masonry. It is also a considerable obstacle to besiegers, as it prevents their ladders for escalade being placed against the escarp.

The profile or section of Vauban’s first system is given in Plate III., fig. 4, in order to illustrate the relative relief or height of the respective works, and to show the command which each has over the work in its front. When the height of the rampart, including that of its parapet, is 20 feet, and that of the parapet of the covered-way is 9 feet above the plane of the site, then the rampart will have a command of 20 feet over the country, and 11 feet over the crest of the covered-way; and the latter, again, will have a command of 9 feet over the country. There are three sorts of command, namely, in front, in rear, and in enfilade, That in front is when any eminence which commands the work directly faces it; that in rear when the eminence is behind the work; and that in enfilade when the eminence is on the prolongation of any line or work. The last, which is the most dangerous kind of command, is best remedied by raising the salient of works exposed to it (see fig. 23, p. 427), or by erecting traverses. In fig. 4 of Plate III. a line, called the line of site, and supposed to be the surface of the ground on which the fortification stands, is drawn, and perpendiculars are erected on it equal to the respective heights of the different parts of the works corresponding to the lines in the figure;— a showing the terrepleine, b the banquette or step to enable the soldiers to fire over the parapet, c the parapet, d the revetment, e the escarp, f the counterscarp, and so on.

2. Vauban ’ s Second and Third Systems.

The principles of Vauban’s First System having been thus explained, no great difficulty will be experienced in understanding the methods of other engineers who have constructed works varying but little in essentials from this system, the variations having arisen from difference of situation and local peculiarities rather than from other causes. In his other methods of construction, as, for example, in his second and third systems, Vauban himself merely modified, according to circumstances, the principles upon which his first is based. When this celebrated military engineer was called upon to repair or improve the fortresses of Landau, Breisach, &c., and found these places surrounded with strong walls strengthened by small towers at the angles, he did not destroy these defences, but constructed, nearly in the same proportions as in his first system, large counterguards or bastions in front of the towers which crowned the angles of the wall, just as the Italian Castriotto had done in 1584. And by this method an important object was attained; for, as in front of each tower, or rather tower-bastion, there ran a ditch which ent off all communication between it and the counterguard, so the enemy, even if they should have succeeded in establishing themselves in the counterguard, would still have another ditch to cross, and another wall to breach, before they could attempt to give the assault.

There is so little difference between the second and third systems of Vauban that a description of the former will enable the reader to appreciate the peculiarities of the latter. In the second system (Plate III., fig. 2), the interior side of the polygon, from the centre of one towerbastion to that of the next, is supposed to be 240 yards, and at 24 yards from its extremities perpendiculars are erected equal to 36 yards for the flanks of the towerbastions. A line is then drawn through the extremities of these perpendiculars, parallel to the interior side AB, till it meets the oblique radius of the polygon, or line drawn from the centre of the polygon bisecting its angle, and this being done on both sides of the angle forms the tower-bastion. The oblique radius is produced 78 yards, and lines of defence are drawn to the angle where the tower-bastion joins the curtain or line AB. On these lines of defence, the faces of the counterguard, or exterior bastion, are set off equal to 128 yards, and from the point forming the shoulder, flanks are directed to a point set off on the line AB, at the distance of 70 yards from its extremities. From the salient angles of the tower-bastions arcs are described with a radius of 14 yards for the breadth of the ditch, and tangents to these arcs are drawn parallel to the faces of the tower-bastion, but stopped where they would meet a line drawn from the salient angle of the tower-bastions, at the distance of 20 yards from the flanks.

The tenaille is the same as in the first system, excepting that at its ends it is carried down till it meets the lines of defence drawn between the flanked or salient angles of the tower-bastions. The ditch in front of the counterguards, or, in other words, the main ditch, is constructed in the same manner as in the first system. The ravelin is formed by setting off 90 yards from the re-entering angle of the counterscarp, and directing its faces to points set off on the counterguards, at the distance of 20 yards from the shoulders. A flank is formed by cutting off the corners of the ravelin at the distance of 14 yards on its demigorge, and 20 on its face; and this flank serves for the placing of guns in such a manner that their fire may be directed into the counterguard, or into the ditch before them, as occasion may require. Again, at the distance of 48 yards from the re-entering angle of the counterscarp, lines are drawn parallel to the faces of the ravelin for the redoubt; a ditch is formed in front of this, and parallel thereto, about 18 feet in breadth; and the redoubt thus constructed has a command of 4 feet over the parapet of the ravelin, as the tower-bastions have over the counterguards. The covered-way and glacis are formed as in the first system. It sometimes happens that redoubts are constructed in the re-entering places of arms; in which case their demigorges are made from 15 to 40 yards, and their faces set off at an angle of 100°, as before.

3. Carmontaigne ’ s System.

The difference between the Systems of Vauban and Cormontaigne may easily be discovered by an examination of Plate III., fig. 3. Vauban makes the faces of his bastions two-sevenths of the exterior side, and Cormontaigne one-third. Vauban, in his first system, directs the faces of his ravelin to points upon the faces of the bastion distant 11 yards from the shoulders, and in his second and third systems, to points distant 20 yards; but Cormontaigne makes the capital of his ravelins about 120 yards, and directs the faces to points distant 30 yards from the shoulders; by which means the flanks are better covered, and the bastions and ravelins are enlarged And this is an advantage; for he is thus enabled to construct a larger redoubt in his ravelin, the curtain and flank are also better covered, and, as the former is shorter, communications are more easily kept up between the bastions. Cormontaigne gives the same breadth to his covered-way as Vauban, but he arranges in a different manner the communication round the extremities of the traverses, as may be seen by inspecting the plate. By this zig-zag line of communication, which resembles the crémaillère trace adopted by Speckle in his covered-way, the passage round the extremity of one traverse may be defended by the fire of the other in its rear, or nearer to the body of the place, and the advance of assailants along the covered-way checked. As Speckle planned in 1589, or long before the invention of ricochet fire by Vauban had rendered traverses an essential element in fortification, his object was not the same as that of Cormontaigne, but simply to ensure a more perfect flanking defence of the branches of the covered-way than that afforded by the places of arms of his systems. The ditches •are, as shown in fig. 3 of Plate III., on different levels— the main ditch being about 23 feet deep, and the ditch of the redoubt of the ravelin only 7 feet, so that from this latter ditch there is a fall of 16 feet to the main ditch, rendering it impossible to attack the ravelin by its gorge without the aid of ladders. An examination of the several figures which represent Vauban’s and Cormontaigne’s systems, as also the outworks of fig. 3, Plate IV., will at once render evident the vital defect of the ordinary arrangements of outworks—that they expose through the openings of their ditches the escarp of the body of the place, or of the work on which their faces or branches are directed, to be breached. In the System of Cormontaigne, as well as in the Modern System next to be considered, the increased projection of the ravelins, by throwing the intervening bastion into a deeply re-entering position, secures it from attack by approaches until the salients of the ravelins have been taken; but this great advantage is diminished by the power of breaching the bastion from the glacis through the opening afforded by the ravelin ditch. For the purpose of covering the communication to the re-entering place of arms, a demi-caponnière, or work composed of a parapet and glacis, was thrown across the ditch of the ravelin, as shown in the figure of the modern system (Plate IV.,fig. 2). This work afforded cover also to troops assembling preparatory to a sortie upon the enemy when making the passage of the ditch, but, from the depth of the ravelin ditch, it was insufficient to mask the revetment of the bastion behind it. It will presently be shown how this object was afterwards effected; and it may be said that without any material change in system, Cormontaigne’s variations from Vauban’s trace are unquestionable improvements

4. The Modern System.

The Modem System, which is shown in Plate IV., fig. 2, varies little from Cormontaigne’s. Its perpendicular is one-sixth of the exterior side, and the faces of the bastions are one-third. The flanks are at right angles to the lines of defence, whereas in Vauban’s System they form an angle of about 82°,—which is not so good, because, in the Modem System, the guns placed in the flanks can fire straight along the ditch without being moved or turned on their platforms. The ravelin is formed by setting off points 34 yards from the shoulder along the face of each bastion; a line joining these points is the base of an equilateral triangle, the vertex of which, opposite the centre of the curtain, forms the salient angle of the ravelin. The redoubt of the ravelin is formed by drawing its faces parallel to those of the ravelin from the shoulder of the parapet of the bastion; and it has flanks with a ditch about 20 yards in breadth. The cavalier in the bastion is drawn parallel to the faces of the bastion, at the distance of 48 yards from them. The ditch of the faces is 10 yards in width, but there is no ditch to the flanks. In bastions strengthened by a cavalier retrenchment, a coupure is formed perpendicularly across the faces of the bastion; the ditch of the coupure is 30 feet wide, and the counterscarp is traced from a point 36 yards from the shoulder of the bastion to meet the counterscarp of the ditch of the cavalier. This system originated in the school of military engineering instituted at Mézières in 1750, and was for some time called the system of the school of Mézières. It has, however, been much improved since; and the system which is now recognized as the “Modern System” is that of General NoizeL Referring, however, to fig. 2 of Plate IV., it will be seen that coupures have been introduced in the faces of the ravelin; and as the ditch of the ravelin in this system is less by 7 or 8 feet than the main ditch, there is a sufficient fall be tween the two to check the enemy in his passage to the latter, whilst the demi-caponnière is raised so much higher, and therefore begins to mask more effectually the revetment of the bastion. In General Noizet’s system this demi-caponnière is formed into an elevated mask, which tends to secure the revetment from the breaching effect of the fire from the enemy’s battery on the crest of the ravelin glacis. This is shown in fig. 63; and the system modified from the former modern system in this respect, as well as in other arrangements, is now the normal bastioned system of the French schools. In General Noizet’s arrangement the flanks are not made perpendicular to the lines of defence, but, as in Vauban’s first system, form angles of about 80° with them. In the citadel of Ghent, which is a beautiful example of this system, but with still further modifications, the retrenchment of the bastion is so formed as to take advantage of this construction; and the flanks, being casemated and pierced in both directions, become on one side the flanks of the retrenchment, whilst on the other they are the ordinary flanks of the bastion, thus giving a much longer curtain to the retrenchment, which occupies the whole gorge of the bastion, than in the form exhibited in fig. 2 of Plate IV.

5. Outworks.

Plate IV., fig. 3, shows several kinds of Outworks, as a horn-work g, tenaillons k and k, a bonnette d, lunettes a and d, an entrenched bastion e, a batardeau ∕, and a caponnière h. These, and other works of a similar description, are constructed for the purpose of occupying ground which might otherwise be of service to the besiegers, or, as in the caponnière, to cover communications; but their application must of course depend upon localities, and the judgment of the engineer must therefore determine in each particular case, which are the best to adopt.

Pqlygonal or German System.

The Systems of Fortification of which mention lias been made were devised to meet the attack of horizontal fire, but henceforward the efforts of the engineer must be directed to devise methods of protection against curved and indirect fire of greatly increased range and power. It is true that the efforts of the later engineers have been in this direction, but the recent introduction of rifled guns and the still more recent development of indirect fire have rendered a recourse to very different measures absolutely necessary.

^Before entering upon the consideration of these measures, it may be well to point out that a rigid adherence to the theory of defilade, which is based on the erroneous supposition that the path of projectiles is in a straight line, and, as a consequence, that artillery can only strike that which it sees, has contributed more than anything else to detain the art of defence behind the art of attack; indeed engineers of great weight were wont to maintain that, if the cordon of the escarp were in the plane passing through the crest of the glacis, the escarp was perfectly covered from artillery fire. Cormontaigne and Montalembert have fallen into this error, and so in more recent times have Choumara and later writers upon the Polygonal System.

The increase in the weight, range, and energy of projectiles, the greater accuracy of fire, not only direct, but indirect, curved, and vertical, the enormous increase in the numbers of armies, and the wonderful mobility afforded to them by the development of railroads and steam vessels, by the subordination of steam, machinery, telegraphy, and other scientific applications of modern life, to military purposes, have rendered necessary fortresses of an enlarged and of a more expensive nature, and have led to the adoption of a system of defence more simple, and based upon broader principles.

The Bastioned Trace designed to afford from uncovered flanks a complete defence to the escarp of the body of the place can accomplish this end no longer, since these flanks Power of English Siege Artillery. [table]

N.B. —The penetration of the siege howitzers is comparatively small. The lowest effective velocities against revetments are considered to be from 450 to 500 feet a second.

can now be destroyed by the fire of distant artillery, and the faces of the bastions themselves can be ricochetted from an equal distance.

, Moreover, this trace, in which the relations between the length of the front, the depth of the ditches, and the command of the enceinte are obligatory, is difficult of application, and weak in its direct artillery defence, inasmuch as a portion of the rampart which should be available for the defence is withdrawn for the service of the flanks and curtains.

In the Polygonal Trace,—which requires no inter-relation between the length of the front, the depth of the ditches, and the command of the body of the place, in which the exterior sides may at pleasure be longer or shorter within the limits of musketry fire, and the line of parapet may be independent of the line of ditch,—these defects disappear, and its application to every variety of ground is more easy and more economical. As, too, the flanks are entirely protected from distant fire, and the faces are not exposed, or are far less exposed, to ricochet than in the angular traces, the polygonal trace offers greater facilities for the employment of artillery as the principal arm of defence, while it has yet another advantage, viz., that its communications are far more simple.

The main difference between the Polygonal and the Bastioned Systems lies in the arrangements for the defence of the ditches. In the latter it is provided by the flanks of the bastions, in the former by caponnières, powerful casemated works, constructed across the ditches. In the flank of the bastion the guns are exposed, and limited in number by the length of the flank; if the flank be lengthened, the face of the bastion must be shortened, thereby diminishing the direct artillery defence of the bastion, or the flanked angle of the bastion must be diminished, rendering the faces— already too liable—still more liable to enfilade. Moreover, a second or lower tier of casemated guns cannot be added to the flank of the bastion without the suppression of the tenaille and consequent exposure of the curtain; whereas the caponnière may be increased in length to any reasonable extent, and may be in two tiers. Again, in the bastion the flank is enfiladed by direct fire on the adjoining face, and is taken in reverse by the enfilade of that face, and by the direct fire against the opposite face and flank. Lastly, in the Polygçnal System a direct fire can be given upon the capital of the angle, while in the Bastioned System this capital is undefended.

The advantage of this system in direct artillery defence appears to be 100 per cent 1 Brialmont—no mean authority —states it at from 25 to 60 percent, or even 100 percent, if the artillery of the outworks is left out of calculation. In a comparison of the fortress of Posen, which is a faulty application of the polygonal system, with an equally strong fortress on the bastioned system, it has been calculated that the siege park of a besieging army would require 20 per cent, more guns for the attack of the former; and the writer goes on to state that more siege materials, a greater development of batteries, a greater number of troops, and a larger park are necessary for the attack of the polygonal as compared with the bastioned system.

Unquestionably, long exterior sides are advantageous for fortresses; and admirably, as has been shown, as the polygonal trace is adapted for fortresses, it is equally well adapted for detached forts, which are often so small that the bastioned trace is inapplicable to them.

The most complete application of this System to a great fortress may be seen in the enceinte of the new fortress at Antwerp, one front of which is shown in Plate V.

In this enceinte the main ditch is wet and wide, and flanked by a powerful central self-flanking caponnière; the flanks are retired and protected by orillons, and the curtain between the latter is broken into two half curtains, separated by a defensible barrack, which forms a retrenched cavalier. The central caponnière is separated from this curtain by a ditch; it is, moreover, covered by a counterguard of two branches, revetted with a loopholed counterscarp gallery from which the countermines diverge; this is further covered by a ravelin of two branches, terminating at the salient in a powerful reverse casemated battery; the ditches of the ravelin are flanked by low casemated batteries. The exterior side is 1100 yards long, the perpendiculars from the centre of this side marking the saliency of the caponnière and the retirement of the centre of the curtain are 104 yards and 71 yards long respectively. The curtain is 250 yards long; the flanks, which are not straight, are formed of two sides, 34 yards and 12 yards long. The flanks of the caponnières are 27 yards long. The salients of the counterguard and ravelin are 190 yards and 295 yards in advance of the exterior side, and the branches of the latter are directed upon points on the exterior line 245 yards on each side of its centre. The front of the defensible barrack is covered by the central caponnière, and the flanks are 84 yards long, forming angles of 100° with the front. The main ditch is 88 yards wide at the salients, and 55 yards wide in front of the orillons; the ditch of the ravelin is 66 yards wide at the salient, and 55 yards wide at the low casemated batteries of its flanks. The ditches are unrevetted, with slopes of two-thirds, except at the head of the central caponnière and in front of the curtain and flanks; the depth of water in them is 10 feet, and its surface is 6 feet below the plane of site; the berms of the enceinte and of the ravelin are 16 feet and 6 feet wide respectively. The command over the country is, in the body of the place, 32 feet at the salients, falling l¾ feet to flanks and curtains, in the ravelin 15 feet, in the counterguard 21 feet designed that the outworks may not obstruct the fire of the body of the place; in the cavaliers of the salients the command rises to 41 feet The parapets are slight, not more than 27 feet thick, but they have very wide terrepleines, and are provided with hollow traverses and large bonnettes. The ramps leading to the terrepleines are unusually wide. The guns are either on carriages firing over a 5-feet parapet, or on siege carriages firing from raised gun banks. The armament is heavy, especially in the central caponnières and flanks; in the former, 22 guns on each face, viz., 16 in casemates and 6 in open battery above, in the latter, 14 guns in two tiers. The ravelin has in addition to the guns on its faces 8 casemated guns in its reverse battery of the salient, and 12 casemated guns in its two low batteries; and provision is made for armouring the embrasures of these. The covered way is 22 yards wide in front of the body of the place, and from 9 yards to 15 yards wide in front of the ravelin. The communications with the country are wide and ample, two through each front; they are also level, very direct, and convenient for sorties.

Epitomized as this description has necessarily been, it will be seen that advantage has been taken very skilfully of a low site and wet ditch, which while offering serious obstacles to the enemy impede as little as possible the offensive operations of the defenders. For the effective defence of the fortress, however, a strong and well-handled garrison, prompt to assume offensive measures, and a large armament are necessary.

The city of Antwerp, Plate VI., lies upon the east bank of the Scheldt, and was originally closely girt by works of the bastioned trace, of which the last remnant, viz., the old citadel, which joined the new enceinte to the river on the south west, has recently been removed. This enceinte consists of 11 fronts of polygonal trace in two lines, of which the 6 on the south and east line are about 2300 yards, and the 5 on the north line are about 1800 yards from the town, and are closed upon the river to the north by the new citadel, a work of considerable size and of the polygonal trace also. The fronts are about 1100 yards long, but the two lines join in rather an acute angle; and to compensate for the weakness of the enceinte at this angle, an advanced ravelin has been constructed on either side wshich prevents the lines from being enfiladed. The length of the enceinte is about 7 miles; butas this line of defence would not keep an enemy beyond bombarding range from the town, a line of 8 detached forts has been censtructed about 4000 yards in advance of the enceinte. 2 These forts, also of the polygonal trace, are placed about 2200 yards apart; they close on the river on their right, and, extending over a circle of about 10 miles, rest upon an inundation on their left. Both fronts and forts are very strong, and form a great intrenched camp of about 17,000 square acres in extent The forts are of the same trace, have wet ditches about 50 yards broad, unrevetted scarps, and bomb-proof accommodation for 1400 men in each; so that to fully garrison the enceinte and the forts about 25,000 men are required. On the west side the river runs in a deep re-entering angle towards the city, and four forts about 2200 yards apart close the space between its bends, and form a very strong defence, placing the city upon this side out of reach of the assailant’s fire.

In England the polygonal trace has of late years been habitually adopted as the most suitable for general purposes, but it has not hitherto been found necessary to have recourse to a regular and continuous system of fortification, the insular position of the country, and its predominating strength at sea, calling merely for the fortification of the principal dockyards and military ports, and for the defence of the more important and more exposed harbours. The defence of the military ports is partly on the water and partly on the land, and has been so arranged in the more important ports that they form large naval an<l military intrenched camps. See Plate VII.

As with modern artillery bombardment is practicable at distances of from four to five miles, the works of defence

The German engineer Rimpier, writing in 1673, says that, not being agreed with respect to principles, engineers have disputed about insignificant details, while they have neglected two most important conditions, protection for the garrison from the besiegers’ fire, and the concentration of a more powerful fire upon the besiegers.

2 A second and still more advanced line of detached forts has been commenced considerably in front of this line.

have been disposed with a view of keeping an enemy at not less than that distance from the dockyards.

Upon the sea fronts the works consist generally of isolated forts, placed, according to the width of the channels, at intervals of 1500 to 2500 yards; these forts, being exposed to the very heavy rifled guns which form the armament of the largest iron-clads of the present time, are protected with shields or walls of iron upon their sea fronts, and when they stand alone in advance of the channel are constructed with a continuous iron wall. The various modes in which the iron composing their armour is disposed will be discussed in a future paragraph. The power of heavy rifled guns is shown in accompanying table.

Upon the land fronts the forts are ordinarily placed at Table showing the power of the present English Armour-piercing Guns, and of a few of the corresponding Foreign Guns. [table]

intervals of about 2000 yards, though these intervals vary according to the nature of the ground. Where the ground is uneven they are smaller, but where the ground.is level 2000 yards should be the least interval, and the forts should be of considerable size; beyond this distance the movement of troops becomes indistinct, and the support afforded by one fort to another is lessened, especially at night and in thick weather. A strong reason for constructing large rather than small forts is that at night or in thick weather offensive measures may often be resorted to with the happiest results. But the garrison of a small fort can never be in a position to undertake such measures; it must always restrict itself to a passive defence, whereas the garrison of a large fort will be able to act offensively, will be in better heart, and better commanded. Brialmont, speaking of small detached forts, says that one of the inconveniences of works of mutual defence is to require a great number of commandants, while in the best armies the men fit to command a fortified place are few.

The trace of these forts is very simple. It ordinarily consists of five sides, the longest of which fronts the enemy; the flank defence of the ditches is provided by three caponnières, one in the middle and one at each extrem ity of the front face. The ditches are deep with good scarps, and the defensive power is increased by a keep, which is separated from the fort by a ditch. There is sufficient bomb-proof cover for the garrison and munitions of war, and the faces are well traversed, while special arrangements are made for the service of the ammunition. The general arrangements may be readily perceived by a reference to the accompanying plan (flg. 64) and sections (figs. 65, 66).

Between the land fronts and the sea fronts the circle of defence is completed by coast batteries. These batteries, which are constructed of earth, concrete, or granite, are of various types, with embrasures protected by iron shields when neaι∙ the sealevel, but when upon heights not below 100

feet above the sea level, with unbroken parapets, the gun firing over a height of 4 feet 3 inches, the cover for the gun detachment being provided by a “sunken way,” 3 feet 9 inches wide and 2 feet 10 inches deep, between the platform and the parapet. Over this sunken way, which is provided with rails, a “loading stage” travels, upon which the charge is brought immediately under the muzzle of the gun.

Though at this and heights above it the “sunken way” affords fair protection to the gun detachment, except at the period of loading and pointing, yet, at these periods, the men employed upon these services are highly exposed, and at all times the gun itself stands high above the parapet, and offers a good mark to an enemy’s ship. Some form of “disappearing carriage? upon which the gun is raised above the crest of the parapet at the moment of delivering its fire, and falls by the force of its recoil to a safe position for loading below the parapet, has long been sought for by artillerists. Such a carriage was proposed by Corneille Redeichkeit in 1775 for the defence of the covered way; but his system, which depended on cords and counterweights, was too cumbrous to move from place to place, and liable to be readily put out of order, and was abandoned. Other inventors endeavoured to attain the same end by the use of eccentric trucks and axletrees so disposed that the gun was on the greater axis for firing, on the smaller for loading; but the difference between the heights of the gun in the two positions was so small that this idea was also abandoned. Two guns were next yoked together by ropes, so that one falling from the firing to the loading position raised the other from the loading to the firing position. General Chasseloup, who proposed this twin-gun system, was occupied thirteen years upon its consideration; and though a mode proposed by him, by which one gun recoiling down one inclined plane drew its twin-gun up a similar adjoining inclined plane, was tried with some success at Milan, it does not appear to have been adopted elsewhere. The matter then rested until Moncrieff produced his counterweight carriage, in which the recoil, while carrying the gun and carriage under cover to the position for loading, raises and holds up, by means of elevators, a heavy counterweight; this counterweight, when the time for firing arrives, is set free, and by its descent raises the gun to the firing position over a parapet 9 feet high, behind which the gun detachment find ample cover—one man only being exposed while laying the gun. The main objection to this system is the great weight of the accessories, which for the 7-ton gun amount, including the carriage, to 20 tons. This has rendered it impossible to apply this counterweight system to guns larger than 7 tons, and even to these its application is very limited. This system is costly and difficult of execution as compared with barbette batteries, and as compared with casemated batteries is far less secure against plunging and vertical fire, which cannot fail to strike some one of its many parts, a slight injury to any of which must put the gun out of action. It is asserted by its partisans that it can be applied to hill sides, so that the presence of a battery of such guns shall be undiscernable by an enemy; but this assertion is not well founded. So much skilled labour is required for the construction of Moncrieff pits that they cannot be improvised, and when made they are by no means invisible. This system has been used to a limited extent by Great Britain, but has not been adopted in other countries. Brialmont, after describing it, says, “We should not be able to share the infatuation for the Moncrieff carriage which has been manufactured in England”; and, he adds, it is easy to foresee that the earth and rubbish which will be thrown into the battery during the combat will render the working of it slow, difficult, and, in some cases, impossible. Certainly the carriage is complicated, and could not be repaired during action.

In earthen batteries protected with iron shields the parapets between the guns are comparatively weak, and, if they be increased in thickness so as to afford sufficient protection, they trench upon the interior space, and interfere with the service of the battery. The parapet can, however, be strengthened by the insertion either of blocks of cement concrete or of plates of iron.

But as under given conditions the disposition and thickness of armour plates remain the same whatever be the nature of battery or fort in which the armouring is placed, the mode only in which the armouring is fixed being varied to suit the circumstances of each particular case, it will probably best meet the purpose of the present paper to give a short summary of the rise and progress of iron armour in its application to works of defence, illustrated by drawings of the most recent construction of each type of work.

Attention first began to be directed to the application of iron to works of coast and harbour defence about the year 1860. At that time armour was being extensively applied to ships of war, and the manufacture of rifled guns had received considerable development, but iron had not been employed for the protection of defensive works, and nothing was known as to the best principles of construction for iron defences or for the capability of this metal for resisting heavy blows. It was soon perceived that it was necessary to have recourse to experiment in respect to every detail of material and construction, and it was laid down as a fixed rule that no detail should be adopted until it had obtained the stamp of experience. Previous to the period of which we are treating an advance in this direction had been made in America in 1855, by the application of metal (lead) concrete to masonry embrasures (but this did not withstand the smooth-bore guns of that day), and at Portsmouth in 1859, by the construction of an embrasure shield, 14 inches thick, of rolled iron bars, which opposed a fair resistance to wrought iron shot from the 68- pounder smooth-bore gun, the most effective gun at that date. In 1860 the most important of the preliminary trials took place against an ordinary embrasure with an iron throat 8 inches thick. The guns used were the 40-pounder, 80-pounder, and 120-pounder (shunt) Armstrong rifled guns, and the 12-ton gun, with cast iron shot. The embrasure gave way, and it became apparent that the accuracy of rifled guns rendered splayed embrasures inadmissible in such positions. About this time, too, experiments with plates of various thicknesses in different positions—vertical, and inclined at angles varying from 10° to 60° with the horizon—showed amongst other results that a given mass of armour plates in a vertical position offered as much resistance as the same mass disposed over the same vertical height in an inclined position. In all these experiments the backings and fastenings occupied important positions. Targets were accordingly made with elastic backings, without elastic backings, and with compound backings of various kinds; but the general result of trials against these targets was to establish the advantage of elastic backings. The armour plates were fitted mechanically without bolts or rivets, were fastened with bolts, and were fastened with continuous rivetting round their edges; the result of the experiments established the superiority of bolts as fastenings for armour plates. Many more experiments had, however, to be made before the proper form of bolt was settled; these were by no means the least interesting of the experiments made in working out this subject, but space does not avail to give the history of them here; and it may be sufficient to say that a bolt has been adopted about 3 inches in diameter in the shank, or rather less than the lesser diameter of the screw, which has a rounded thread (about 6 to the inch) and a shallow rounded cut; that the bolt holes are made one inch larger in diameter than the bolts; that the edges of the holes are coned, and that cupped washers receive the nut on the inner end, which is cupshaped (as is the washer of the front of the bolt) as shown in Plate VIII.; and that various minor arrangements have been made for inducing gradual action, and so relieving suddenness of strain upon the bolt. Finally these bolts are made of special iron of a fibrous nature, and elongating from 35 to 45 per cent, under pressure.

The law of the resistance of armour plates received early investigation during the course of these experiments. Sir W. Fairbairn, supposing that the resistance of armour plates to the impact of a shot was analogous to the resistance of plates to a punch, deduced this general formula (C being made equal to 3,374,900) :—

√WO 2

CR^ *

Sir W. Armstrong endeavoured to ascertain the resistance by the application of the dynamic theory of heat. Captain Noble, R.A., from many experiments, concluded that the penetration of steel shot is directly proportional to the work in the shot, whether a heavy shot with a low velocity or a light shot with a high velocity be employed; and that the resistance of armour to steel shot varied as the I power of its thickness. But Captain English, R.E., who appears to have treated this subject most scientifically, considers that the energy absorbed by a plate in resisting a shot is made up of the energy expended in enlarging an indefinitely small hole through the plate, and of the energy absorbed in frictional resistance, and is equal to the cube of the diameter of the shot multiplied by a constant—a separate constant being required for each proportion to the diameter of the shot, of depth of indent in the one case, and thickness of plate in the other.

Having obtained a law which can be relied upon for thick armour plates (it is not, however, applicable to very thin plates), the mode in which the iron in an armour-plated wall should be disposed, i.e., in one solid plate or in two or three thicknesses of plates, was shortly settled. A comparison of experiments against 7 inches of iron armour plate disposed in one, two, and three thicknesses gave resistances in the proportion of 100, 96, and 89. Further experiments against single and double plates of 5 inches showed that the double plate offered nearly three times the resistance of the single plate; and finally a comparison between a 15-inch plate and three 6 inch plates showed that though the solid plate offered slightly more resistance to a single blow it broke up sooner under repeated blows than did the three plates; but as, of course, there is a limit in manufacture to the mass of an armour plate, it is evident that the thicke.r the plate the more numerous will be the joints in a given area, and if the armour be in one thickness, all these joints are lines of weak resistance. The disposal of the joints, then, is a matter of first importance in designing iron structures, and in this respect the arrangement in several thicknesses, or the plate upon plate system, as it is called, offers the greatest advantage, for the plates can be so arranged that no joint goes through more than one-third the thickness; moreover, this system is more easy and more economical in construction, and can be strengthened with greater facility at any future time.

In order to put the conclusions arrived at to practical test, a shield for a casemate opening 12 feet long and 8 feet high was constructed of three 5-inch plates placed at intervals of 5 inches, the intervals being filled with iron concrete; the plates were whole, each covering the entire opening, and each was bolted to the plate next to it, the inner plate being bolted to the shield frame in rear; the front plate was secured by 10 bolts, the others by 8 bolts each; the total weight of the shield was 56 tons 8 cwt. It was struck with 16 shot from 25-ton, 18-ton, and 14 ’ 5-ton muzzleloading rifled guns at 200 yards distance; the average energy of each blow was 5321 foot tons, and the aggregate 90,000 foot tons,—upwards of 1000 foot tons per foot superficial of the shield’s face; but the shield was not driven out of shape, and its back or interior face was uninjured.

This experiment was so satisfactory in its results that henceforward there was no hesitation with respect to the broad principles of armour construction, and it only remained to adapt these principles to the different cases which presented themselves. These are sufficiently illustrated by the drawings in Plates VIII. and IX. The first is an open battery shield for an opening 9 feet wide and 7 feet high; the second is an ordinary casemate shield 12 feet wide and 9 feet high, and the third is a portion of an isolated sea fort with an exterior iron wall. The application of iron has facilitated improvements in the construction of the roofs of bomb-proof buildings, and the form of roof shown in the sea fort may serve as a model of construction of this kind. It is composed of arch plates of ¾-inch iron curved to a radius of 5 feet 6 inches, springing from iron girders 1 foot 9 inches deep and 1 foot 2 inches wide. The arch plates are covered with brick arches, which are again covered with 3 or 4 feet of Portland cement concrete. This roof is equal to a load of one half ton per foot superficial, with a tensile strain upon the iron not exceeding 5 tons per square inch. Such a roof covered with 5 feet of earth was tested by vertical fire of 13-inch mortar shells at 1000 yards. The few rounds which struck it produced no effect, and after the 298th round practice was discontinued; but the earth was removed, and the bared concrete was struck by a shell, which only produced an indentation of 8 inches.

The cost of iron structures is, however, a drawback to their more general employment,—so much so that only wealthy nations can afford to erect them, and but in limited numbers. The cost of an open battery shield may be stated at £800, its weight 10 tons; of a casemated shield, £1800, its weight 40 tons; of an iron-walled fort, £5550 per gun, its weight 125 tons per gun.

It is, however, to be observed that, in special cases where the forts are constructed in very deep water, and where, consequently, the increase in the quantity of masonry in the substructure becomes very great fcr every additional foot of radius, an iron-walled fort, which admits of the guns being placed in a comparatively very small area, is the most economical method of construction, and that for constructive purposes a circle is the best form of such fort.

In all forts designed for very heavy guns special provision becomes necessary for the ammunition service of the guns. The cartridge and shell stores are kept separate, and are provided in the proportion of one of each for each gun, or each pair of guns. As a rule, these stores are securely placed in the basement under the gun they supply, the cartridges and projectiles being raised by mechanical appliances through “lifts” in the heart of the building to the rear of the gun. The ammunition stores are lighted by lamps placed in “light chambers,” separated from the stores by thick plate glass; these “chambers” are entered from passages entirely distinct from the passages used for the service of the ammunition. The proper organization of the ammunition service is of the utmost importance for the efficiency of the fort; by it the labour of the gun detachment is lessened, and the rapid service of the gun facilitated. Each gun chamber is in speaking communication, by means of tubes, with its own ammunition stores, so that the men in the latter, though absolutely shut in below during action, still form part of their own gun detachment. Finally, the guns of the fort are collected into groups for purposes of command, and the guns of each group are directed from a “look-out” place constructed on the top of the fort, which is in speaking communication with each gun of the group.

It his been found that when armour is struck by a shot, lining of some kind is necessary to deaden the effect of vibration and sound, and to act as a target to receive, and protect the gun detachment from, splinters thrown off from the interior. This lining should be flexible, so that it may be drawn close round the gun while it is being discharged, thereby keeping the smoke out of the gun chamber, may reduce the effect of blast and concussion, and may prevent splinters and balls entering through the port. No material has been found to answer so well as rope, and “mantlets,” as such appliances are called, are now invariably made of this material. The only drawback to rope is its liability to catch fire, but this is entirely obviated by washing it with a saturated solution of chloride of calcium.

There are two other forms in which iron has been applied which should not be passed by without notice, viz., “curved-fronted shields” and “turrets.” In the former the casemate is of the ordinary character, but the shield frame, which is constructed with a sharp curve of 13 feet or 14 feet internal radius, is more diflìcult to make, and more costly. Two ports of the usual dimensions are formed in the shield, and the gun is placed behind it upon a turn-table, on which racers are laid so that the gun will fire through a lateral arc of training of 60° at each port The gun is transferred at pleasure from one port to the other by the movement of the turn-table, and commands an arc of 120°. The weight of iron is 150 tons per gun, the cost £7500 per gun; but in considering the cost of this arrangement it should be observed that by it one gun does the work of two.

In the turret one or two guns are placed in the interior of a cylindrical wall of iron armour closed overhead with ordinary bomb-proof covering. The turret wslth its contents is revolved by steam or other motive power, so that each gun commands a whole circle. Various arrangements have been designed for the service of the gun,—in one the loading is done inside the turret, in another under the glacis, in a third while the turret is being turned to the rear,—but whatever the arrangement, no time need be thereby lost, as the guns may be so placed that one revolves into action, while the other revolves out of action for loading. It would seem that a breech-hading arrangement for heavy guns would lend itself more readily to the turret form of construction. With an armament of breech-loaders, the turret might be reduced in internal diameter; the port opening need be no larger than the chace of the gun, which would not have to be withdrawn for loading, and which is laid by means of a small aperture contrived in the roof of the turret—the man who lays the gun having the machinery under his hand, and “training” the turret and gun himself iu any direction. In turrets provision is made in the basement in the usual way for the accommodation of the garrison, and for the storage and service of the ammunition, as well as for the motive power and machinery. Special arrangements are made for ventilation and for the escape of smoke. The surface of the exterior to a certain distance in advance of the turret is plated with iron and sloped upwards “en glacis,” so as to cover the base of the turret, and protect the turning gear from dislocation under the blows of heavy projectiles. See Plate X., fig. 1.

Before quitting this subject it may be well to offer a few remarks on the employment of cupolas or turrets on land defences. Either of these forms of iron construction may be advantageously employed in advanced positions where it is necessary to retain guns until the very last—such as the salients of ravelins, and in the angles of fronts of fortifications; also in points which are commanded from heights in their vicinity. As these constructions are indestructible by the direct fire of siege guns, and are absolutely safe from enfilade and reverse fire, they confer very great advantages upon the defence. They should mount heavier guns than can be brought against them; they cannot be silenced by the concentration of any number of light guns, and, judiciously used, they should place the artillery defence above the artillery attack. They render the construction of the first batteries of attack far more difficult, and force them to open at a greater distance from the place; and, at any period of the attack, they can meet its artillery with heavier metaL The guns of the attack are practically limited to about the calibre of the 64-pounders, and comparatively light armour will withstand these, and will preserve in security and render more easy the service of guns at least two calibres higher. Such constructions have been made by the Belgians in the detached forts round Antwerp and in Antwerp; by the Germans in the detached forts round Metz and in Metz, on the Rhine, and on the Weser; and by the Russians. In England there has as yet been no occasion to resort to them.

In some at least of the places mentioned above, a system of construction and a material advocated by Grusen have been employed; a type is shown in Plate X., fig. 2. The plates which are made of chilled cast iron manufactured by the Grusen process, are fitted together, without screws or bolts, in a simple manner. Each plate is a segment of the cupola, and is grooved at the edges; the segments are placed in position, and melted zinc is poured into the grooves, forming a close and solid joint A glacis similarly constructed protects the base, which is set in motion by hand machinery. The interior arrangements do not differ in principle from those described above for turrets. It is said that such a turret weighing 133 tons can be made to revolve round the whole circle by four men in three and a half minutes. Its cost is about <£16,000.

The Grusen metal is reported to have a very hard exterior surface, with great interior toughness and tenacity, and may probably be used with advantage in cupolas for land defence; but the experience in England does not lead to the conclusion that it is a suitable material for resisting the extremely heavy projectiles carried by the war ships of the present day. Particular attention has been directed to the nature and manufacture of armour plates in Britain, and, up to the present time, the results afforded have been most satisfactory. The iron employed is best described in the wording of the specification for manufacture, viz.:— “The plates must be soft, fibrous, thoroughly welded, and capable of offering good resistance to cannon shot, without indication of brittleness, and without the separation of the several moulds of which they may be composed.” This specification was adopted after many experiments with hammered and rolled plates, in which the former, in consequence of the absence of fibre, conspicuously failed in comparison with the latter.

The best material for armour plates is, however, again prominently under consideration; so great an increase in penetration was obtained with chilled iron shot that the manufacture of steel projectiles was stopped as far back as 1866. Great advances have since taken place in the processes by which steel is made, and steel projectiles of great penetrating power have recently i been under trial; by the use, too, of prismatic powder disposed in cartridges with a definite amount of air space, by which the combustion is rendered more gradual and more thorough, a far higher velocity is obtained with a materially diminished strain upon the chamber of the gun. This has rendered it possible to enlarge the chambers of the heavy guns and to increase their lengths by several calibres, with a resulting increase in energy of about one-third, so that a plate which would keep out a projectile of 800 lb weight from a 38-ton gun will now barely keep out a projectile of 400 lb from an 18-ton gun. It is not impossible, however, that by a combination of iron and steel the resistance of armour may be again brought up to the penetrating power of projectiles. During this consideration many curious and unexpected results have been obtained, but they have not been reduced to such a form at present as to modify what is stated above. The whole question is, however, full of interest, and will, it may be anticipated, receive considerable development before long.

Armament of Fortresses.

The Systems of Fortification having been briefly described, it is right to say a few words here respecting the means of defending a place after it has been fortified. It is difficult to lay down exact rules as to the proportion of ordnance, ammunition, and stores of all kinds required for the defence of a fortified place, seeing they must necessarily vary according to the particular situation of each fortress, the system on which its works have been constructed, and the species of attack to which it may be exposed. If, for example, one of the sides be covered by a morass, swamp, or other obstruction which it is difficult or perhaps impossible to surmount, it must be obvious that a smaller proportion of artillery will be required than if the fortress were equally accessible on every side; and, on the other hand, a maritime fortress, accessible at all points, will necessarily require for its defence a larger proportion of ordnance than if it were only assailable on one or a few of these points. Where every front is equally exposed to attack, all must be equally prepared.

On this subject, however, certain maxims have been established, of which the following appear to be the most important. First, the proportion of ordnance, ammunition, and stores should never exceed the quantity necessary for a brave and resolute defence. Secondly, those fronts which are considered the most exposed to attack should be the most completely armed, whilst a partial armament of the remaining fronts may suffice. Thirdly, to the front to be attacked the following pieces of ordnance should be allotted, viz., to each Bastion, 1 for the salient, 5 for each face, 3 for each flank; to the Ravelin, 5 for each face; to the Lunette, 3 for each face, and a few pieces for the places of arms in the covered-way;—so that if one front be completely armed, the proportion of ordnance will be 17 for the Bastion, 10 for the Ravelin, 6 for the Lunette, and 6 for the places of arms,—in all a total of 39 pieces for the front. This proportion is less than has been fixed by many authorities, but the range and accuracy of guns has so increased since the introduction of rifled ordnance that it will be necessary to provide a traverse for every gun on the most exposed faces, and this, while it affords security to the artillery, materially diminishes the space available for mounting guns. It may be thought by some that this arrangement provides too much traverse shelter, but a few well-protected and well-served guns are better than double the number in exposed positions. Fourthly, when a place is exposed to attack on two contiguous fronts, the armament of each should be augmented one-half; when it is threatened with attack on detached fronts, the armament should be doubled. Fifthly, each of the other fronts should merely be provided with such a proportion as to secure it against insult. From this it may be assumed that a hexagon having only one front liable to attack should be completely armed on the two adjoining fronts, and that about seven guns per bastion and seven per outwork will be sufficient for the remaining fronts, and that a total of 178 pieces of ordnance will be sufficient for a hexagon.

The next consideration is the proportion which the several kinds of ordnance should bear to one another. Ordnance of the higher calibres is not the only ordnance which ought to be employed; in many cases medium and light guns are more efficacious; for when only troops or working-parties are to be fired at, light guns will answer every purpose; their range is nearly equal to that of larger guns, and they are more manageable and may be worked with greater rapidity. Short guns of heavy calibre which throw heavy charges of case and shrapnel are best adapted for the flanks; and, generally, the largest or heaviest ordnance should only be employed to destroy the besiegers’ batteries and dismount their guns. The light guns, as they can easily be withdrawn, should be placed in the covered-way, in the places of arms, and in the outworks of every description. The heavy guns and mortars, which are not so easily moved, should be within the body of the place, and as they require large charges of ammunition, they should be less frequently used, and only upon urgent occasions. A judicious economy of ammunition is a duty incumbent upon every commandant of a fortified place. The conduct of General Chassé in the defence of the citadel of Antwerp was a model in this respect. From the commencement till the close of the attack, scarcely a single shot was needlessly expended by the garrison.

Attack and Defence of Fortified Places.

Having brought thediscussion of Permanent Fortifications to this point we may now consider the attack of fortified places, the general system of which was introduced and perfected by Vauban, so that it has ever since served as a model for the plans of his successors.

“La résolution des sièges,” says the Marshal, “estnne affaire de cabinet. Elle est une suite naturelle de la supériorité que l’on croit avoir sur ses ennemis; mais leur exécution étant une des plus sérieuses, des plus importantes, et des plus difficiles parties, elle demande aussi le plus de mesure et de circonspection?’ He then goes on to state that the success of sieges depends on several circumstances, such as “1. Du secret, sans lequel il est difficile de réussir; 2. Des forces que l’on a sur pied pour attaquer les places des ennemis, et défendre les siennes; 3. De la disposition des ennemis; car s’ils sont réunis, et aussi forts que nous, ils peuvent nous empêcher d’en faire; 4. De l’état des magazins les plus à portée des lieux sur lesquels on peut entreprendre; 5. De la conjoncture des tems, parce que tous ne sont pas propres aux sièges, et rien n’étant plus ruineux que ceux d’hyver, on les doit éviter tant qu’on peut; 6. Des fonds nécessaires à leurs dépenses; car l’argent est le nerf de la guerre, sans lui on ne sçauroit réussir en rien. Ce sont là des mesures à prendre de longue main, qui doivent être dirigées à loisir; et apres tout cela, quand on croit les avoir bien prises souvent tout échappe; car l’ennemi, qui n’est jamais d’accord avec vous, pourra vous interrompre. ... 11 faut bien peser toutes ces considérations, avant que de se déterminer; et prendre toujours si bien son teins, que l’ennemi ne puisse vous tomber sur les bras avant vos établissemens.”

A siege, therefore, being one of the most arduous undertakings in which an army can be employed,—one in which the greatest fatigue, hardships, and personal risk are encountered, and in which the prize can only be won by complete victory,—it is obvious that upon the success or failure of such an enterprise may depend the fate of a campaign or of an army, and perhaps the existence of a state. Of this the failures before Pavia in 1525, before Metz in 1552, before Prague in 1557, before St Jean d’Acre in 1799, and before Burgos in 1812 present instructive examples. By the first, France lost her monarch, the flower of her nobility, and all her Italian conquests; by the second, she was saved from destruction, whilst 30,000 of her enemies perished; by the third, the greatest warrior of his age, Frederick the Great, was brought to the very brink of destruction; by the fourth, the most successful general of France, and perhaps the greatest commander that any age or country has produced, was stopped short in his career of victory; and by the last, a beaten enemy gained time to recruit his forces, concentrate his scattered corps, and regain that ascendency of which the victory at Salamanca had for a time deprived him.

It is therefore of the greatest importance to a state that the sieges undertaken by its armies should be carried on in the best and most efficient manner possible, or, in other words, that by a due combination of science, labour, and force these operations should be short and certain, and without excessive expenditure of life. But the sieges undertaken by the British have seldom, if ever, united'these three indispensable conditions; and with regard to those which took place during the contest in the Peninsula, it is well known that defects of organization, particularly the want of a body of men, such as sappers and miners, trained to the labour required at sieges, and an inadequate supply of material, necessitated a partial departure from established principles and rules of attack, which led to a waste of life unprecedented in modern sieges. Till late in 1813 the army had not a single sapper or miner; regular approaches were therefore difficult if not impracticable. It was necessary, in almost every case, to take the bull, as the saying is, by the horns; the last operation of a siege scientifically conducted, namely, battering in breach, was amongst the first undertaken: and the troops, marched to the assault whilst the defences remained nearly entire, were exposed to every species of destruction which the unreduced means of the besieged could bring to bear against them. The army of a country which has outstripped all others in the useful arts and in mechanical improvements was left wholly unprovided with those appliances which at once economize life and labour, and serve to render both most effectual for the purposes to which they are applied. Nevertheless, it may be observed that, in all periods and in all countries, the means employed for the reduction of fortresses have generally increased and become more overwhelming and irresistible in proportion to the advancement of knowledge and to the improvement of the useful arts; and that in Europe during the last two centuries, the extension of wealth and knowledge, accompanied by an unprecedented development of talent, directed towards military movements, has caused the results of sieges, and indeed of almost all the operations of war, to depend much less on individual exertion or casual displays of heroism, than on combination and expenditure. This may be made apparent by a slight retrospect of the sieges of the 16th century.

At the period referred to, the art of disposing the several works of a fortress so as to cover each other, and to be covered by their glacis from the view of an enemy, was unknown; whilst the limited supply of artillery, its unwieldiness, and the great expense and difficulty in moving it rendered it so little available for sieges, that the chief object in fortifying towns was to render them secure against escalade and surprise, by means of lofty walls or altitude of situation. All places fortified prior to the 16th century are invariably of this construction. And as the simplicity of the fortresses to be attacked necessarily gave the same character to the operations directed against them, so, in those days, much was effected by daring courage, without the aid of science; and gallantry in individual combat, or fearlessness in confronting danger, were esteemed the highest qualities of a besieger. Thus contests dragged on for months, in petty þut sanguinary affairs, and the most persevering or the most hardy troops, however ill organized or supplied, were the most dreaded, and not unfrequently the most successful. But when artillery became more movable, and large quantities were employed in sieges, lofty and exposed walls nc longer opposed an adequate barrier; large breaches were speedily effected; places which had formerly resisted for months were carried in a few days; and so, in order to restore an equality to the defence, it became necessary to screen the ramparts from distant fire. The attempt to gain security by concealment rapidly advanced, whilst the means of the besiegers remained the same; and between the middle of the 16th and commencement of the 17th century works were so skilfully disposed and so well covered that the defence of towns obtained a temporary superiority over the attack. Of this the obstinate and successful defences made by the Dutch against the Spaniards during the reigns of Philip II. and Philip III. may be cited as remarkable examples.

The pre-eminence of the defence over the attack was mainly due to the great difficulty of dragging up heavy ordnance with a besieging army, so that, the weight of metal being generally in favour of the besieged, the fire of the fortress was able to subdue that of the batteries of attack. Vauban, however, in the reign of Louis XIV., restored the preponderance of power to the attack by the invention of ricochet fire, as the guns of the besieged were thereby dismounted or disabled at an early stage of the siege, and the besiegers being relieved in great measure from the effects of a direct and powerful fire of artillery, were enabled to push forward their approaches by the sap. Vauban also matured into a system the attack, by laying down rules for the establishment of parallels, for the position of enfilade and other batteries, and for the general conduct of the approaches. The real type of an attack is a moving parapet, the besieger carrying forward with him his cover, and thus depending for his success not so much on his offensive as on his defensive arrangements. It was by this combination of science and labour, aided by the steady advances of brave and well-trained sappers, that the reduction of fortresses which would have resisted for ever the rude assaults of the most determined enemy was rendered comparatively easy and certain.

These increased means of attack, to which it was found impossible to oppose a successful resistance, caused the art of concealment or covering to be further studied, till at length, in well-constructed fortresses, not a single wall remained exposed to view, and the sap and the mine became as necessary as the gun and the mortar to the success of a besieger. To render this intelligible to the general reader, a descriptive sketch of the progress of a modern attack, from the excellent work of Sir John Jones already referred to, is introduced here.

“The first operation of a besieger,” says that able and experienced engineer, “is to establish a force able to cope with the garrison of the town to be attacked, at the distance of some hundreds of yards from its ramparts. This is effected by approaching the place secretly in the night with a body of men, part carrying entrenching tools, and the remainder armed. The former dig a trench in the ground parallel to the front to be attacked, and with the earth that comes out of the trench raise a bank on the side next to the enemy, whilst the latter remain formed in a recumbent posture, in readiness to protect those at work, should the garrison sally out. During the night this trench and bank are made of sufficient depth and extent to cover from the missiles of the place the number of men requisite to cope with the garrison, and the besiegers remain in the trench during the following day, in despite of the fire or sorties of the besieged. This trench is afterwards widened and deepened, and the bank of earth raised, forming a covered road, called a parallel, which embraces all the fortifications to be attacked; and along this road, guns, waggons, and men securely and convenienti}’ move, sheltered from the view and the missiles of the garrison. Batteries of guns and mortars are then constructed on the side of the road, to oppose the guns of the place, and in a short time, by superiority of fire, principally arising from situation, silence all those guns which bear on the works of the attack. After this ascendency is attained, the same species of covered road is, by certain rules of art, carried forward, till it passes over all the exterior defences of the place, and touches the main rampart wall at a spot where it has been previously beaten down by the fire of the batteries erected expressly for the purpose in the more advanced parts of the road.

“The besiegers’ troops, being thus enabled to march in perfect security to the opening in the Avails of the place, assault it in strong columns, and, being much more numerous than the garrison defending the breach, soon overcome them, the more easily as they are assisted by a fire of artillery and musketry directed on the garrison from portions of the road only a few yards from the breach, —which fire can at that distance be maintained, without injury to the assailants, on the defenders of the breach until the very instant of personal contention. The first breach being carried, should the garrison have inner works, the covered road is by similar rules of art pushed forward through the opening, and advanced batteries are erected in it to overpower the remaining guns of the place; which effected, the road is again pushed forward, and the troops march in security to the assault of breaches made in a similar manner in those interior works, and invariably carry them with little loss. But as it is always an object to preserve the life of even a single soldier, so, when time is abundant, the loss of men attendant on the assault of breaches under these favourable circumstances may be avoided, by pushing up the covered road through the breach, without giving the assault, and thus, by art and labour, the strongest defences frequently fall without any exertion of open force.”

From this description it must be obvious that the most important object at a siege is to carry forward the covered road to the walls of the place, that all the other operations are secondary to and in furtherance of such an advance, and that hence the efficiency of armies at sieges depends upon their ability to complete the road at a small expense of life. But as this covered road advances, the difficulty increases. At its commencement, the work, being many hundred yards from the fortifications, can be performed by the common soldiers. But when the road or trench has arrived within a fair range of musketry from the place, then particular precautions are required; yet the work at this stage is not so difficultas to prevent its being executed by soldiers who have had a little previous training. At the last stage, when the approaches have been pushed close to the place, when to be seen is to be killed, when mine after mine blows up the head of the road, with the officers and men on the spot, when the space becomes so confined that little or no front of defence can be obtained, and when the enemy’s grenadiers sally forth every moment to attack and deal out destruction to the workmen,—then the work becomes truly hazardous, and can only be performed by selected brave men, called sappers, who have acquired the difficult and dangerous art from which they derive their name. An indispensable auxiliary to the sapper is the miner, who in the exercise of his art requires even greater skill, conduct, and courage. The duty of a miner at a siege is to accompany the sapper, to listen for and discover the enemy’s miner at work, and to prevent his blovzing up the head of the road, either by sinking a shaft down to and meeting him, in which case a subterranean conflict ensues, or by running a gallery close to that of his opponent, and forcing him to desist from working by means of suffocating compositions, and by various arts the knowsledge of which he has acquired from experience. Without the aid of skilful miners, sappers would be unable to execute that part of the covered road forming the descent into the ditch, not to mention other operations in the progress of which the assistance of the miner is equally indispensable; and without their joint labours and steady co-operation, no besiegers’ approaches would ever reach the walls of a fortress. In the British service they are blended into one honourable body, the Royal Engineers.

But a siege, though it calls for personal bravery, unremitting exertion, and extraordinary labour in all employed, if scientifically prosecuted, is certain in its progress and its result. More or less skill and exertion in the contending parties may prolong or abridge its duration; but the sapper and the miner, when skilfully directed and adequately supported, will ultimately surmount every obstacle. On the other hand, sieges undertaken by armies imperfectly supplied with these auxiliaries are hazardous in the extreme. The only chance of success consists in scrutinizing the exterior of the fortress, in order to discover some spot whence, from the irregularity of the ground, or fault of construction, the main escarp wall may be seen at a distance sufficiently great to enable the ordinary working parties to approach with the covered road, and there to establish batteries for breaching or forming an opening through it into the place. When this is effected, the troops advance to the assault of the breach, as in the 16th century, thus passing from the shelter of the covered road into the fire of the place at the moment when it becomes most powerful and destructive; and as the fire of the besiegers’ distant batteries is necessarily suspended during the assault, lest it should destroy the storming party, the garrison can with impunity mount the ramparts and employ every kind of weapon, missile, and instrument in their defence. All the chances are thus in favour of the besieged; for should the columns of attack, under these disadvantages, arrive in good order at the brink of the ditch, they must descend into it down a wall from 14 to 16 feet in depth, which cannot fail to break their order and throw them into confusion; and as no new formation can be attempted in a spot where death meets them in every shape, the assailants rush to the breach more like a rabble than a solid column. From this moment success hinges on the individual bravery of the officers and men, and the unshrinking firmness of the general commanding, in encouraging and supporting their efforts. But although these qualities, when united in a high degree, may, at a great sacrifice of life, enable the assailants to overcome all resistance, yet an assault of this nature, under ordinary circumstances, has almost always proved unsuccessful. Indeed, it may be laid down as the result of experience that, should an army unprovided with sappers and miners, and with the materials and means to render their services efficient, be opposed to a place fortified according to the modern system, with its walls completely covered, all the usual methods to reduce it would prove unavailing; no period of time nor sacrifice of men would be sufficient to purchase success, and the prudent course would be to decline an attempt pregnant with hazard, perhaps ruin.

“These considerations,” says Sir John Jones, to whom we are indebted for the above account of the various modes of attacking fortified places, “have for many years had their due weight with the great powers of Europe, and have induced them to form and keep up, as integral portions of their military strength, every necessary auxiliary for the reduction of fortresses; and sieges have in consequence become certain and comparatively bloodless. But England, constitutionally jealous of permanent military establishments, has always discountenanced military organization and military preparation till the hour of need, and with respect to sieges, which are rare, and exclusively offensive oι>erations, has even carried her jealous feelings beyond the bounds of rational prudence; for, possessing a corps of officers professionally educated and well grounded in the science of attack and defence, she has denied them every requisite establishment to render their acquirements availing, and has most unreasonably expected her armies to reduce the skilfully fortified and well-covered places of the 19th century with means inferior to those used against the exposed and ill-constructed places of the 16th and 17th centuries.”

And what was the immediate consequence of this irrational jealousy and niggardly parsimony? Contrary to all ordinary calculation, the fortresses garrisoned by the French in Spain were reduced; but at what a prodigious expenditure of life was this effected! In the several attacks upon Badajoz, two of which from extrinsic circumstances proved abortive, a little army was sacrificed; as many men, in short, as would have been sufficient for ten sieges undertaken with adequate means, and conducted according to the ordinary rules of science. But this is not to be understood as involving any reflection on the military talents of the general or the professional ability of the engineers. General Foy, in his work on the war in the Peninsula, has indeed made such a charge, condemning the mode of attacking fortresses adopted by the British in Spain as unskilful and inefficacious, and bringing it forward as indisputable proof of the low state of their military knowledge. But it should be recollected that the adoption of this mode was not a matter of choice, but of necessity, and that, if it was in its nature rash, hazardous, and inefficient, the fact of its having been directed against Ciudad Rcdrigo and Badajoz with such rapidity of development and certainty of result as to outstrip the calculations of the French marshals, deceive the vigilance of French governors, paralyse the science of the French engineers, and baffle every defensive effort of the French garrisons, is surely no evidence of deficiency in military talent and professional skill. The objections to this mode of attack are insurmountable and decisive; that it succeeded in the instances referred to is merely a proof of what British soldiers, even when acting under the greatest disadvantages, are capable of accomplishing. These remarks are, however, no longer applicable. Since the Crimean war great attention has been bestowed upon the education and training of sappers and miners, and though England has neither the numbers of men nor the quantities of stores possessed by Continental nations, yet what she has of each is of the best. Every advance in science, if applicable, has been at once adopted into the military service; and as our civil engineers are as a body admittedly without superiors in the civil world, it may be confidently stated that in the military world our military engineers hold no inferior position.

Having thus given a general description of the methods of attack, we shall now subjoin, on high authority, a view of what is considered necessary for the proper defence of fortified places. An order issued by the French minister of war in 1813 contains directions on the subject which are almost universally applicable, and therefore deserve a place here. Every commander is directed to consider his garrison as liable to be unexpectedly attacked, and to pass at once from a state of peace into a stats of war or siege, either by rebellion, by unlawful assemblies, by the presence of an enemy, by surprise, or by sudden assault,—in a word, by unforseen causes, of which the history of war offers numerous examples. He is therefore ordered, even in time of peace, to fix his plan and arrangement for defence, according to such supposed attacks as may appear most probable» and to determine, for the principal cases which may be likely to occur, the necessary posts, reserves, and movements of the troops, and to take, measures to ensure the due and active co-operation of every corps of the garrison. He ought, particularly, to make himself, thoroughly acquainted with (1) the ground beyond the place which may be within the circle of action, of investment, and of attack; (2) the fortifications of the place, its interior, its buildings, its military edifices or establishments; (3) the garrison, the means of the place in artillery, in ammunition, and in other stores of every kind; (4) the population to be maintained in time of siege, the men capable of bearing arms, the master and journeymen artificers fit to be employed either on the works or in case of fire; and (5) the provisions, materials, tools, and other resources which the town itself and surrounding country can furnish, and which it might be necessary to secure in case of siege. In order to enable governors and commanders to comply with these instructions, which are clear and precise, the minister proceeds to detail their principal duties, according to the circumstances in which they may find themselves placed; but for these we must refer to the general order itself, which is a masterpiece of its kind, and in all probability emanated directly from½Napoleon himself. Its object appears to have been to inspire a governor with hopes that, by taking proper precautions, and making a full use of means previously provided, the defence might be rendered equal, if not superior, to the attack; and whether this be so or not, the importance of the directions embodied in the order is not diminished, and where they are duly observed the nature and extent of the resistance must be materially increased.

The protracted and able defence of Sebastopol led many to imagine that the Russians by new defensive arrangements had solved the problem so long under discussion, and had again restored to the defence much of its former superiority over the attack. But the real merits of the Russian engineers consisted not in the discovery of new principles, but in the skilful application of those principles which, recognized at an early period, have been by degrees matured and enlarged. In estimating the comparative results of the attack and defence of Sebastopol, it must be remembered that neither can be judged by strict rules, as neither conformed to such rules. The north side being left open by the impossibility of investing both sides, the south became a detached line of powerful intrenchments, to the defence of which the whole force of an army, not a garrison, could be directed at will. The strength of the garrison, continually renewed from without, permitted the fullest use of detached works, which, when backed by a line in rear sufficiently strong to resist a coup-de-main, constitute one of the most powerful modes of defence. Such a fort or work was the celebrated Malakoff Tower, and the redoubt enveloping it, the type of which may be found in the lunette of Darçon, of which fig. 67 is a plan. In this lunette, intended to be prepared before-hand, T is a powerful tower, LL a lunette, which in this case is revetted, but might have been made, as at the Malakoff, a simple earth-work— c an underground communication to g,g, loopholed galleries for flanking the ditches. This sketch will show the general principle of defence involved in such works, but of course the form must vary in the hands of an able engineer, to suit the peculiarities of the ground. At the Malakoff the redoubt was made circular, but in principle it was strictly analogous to the lunette.

Siege of the Citadel of Antwerp.

We shall now, as an example, give a sketch (abridged from the United Service Journal) of the attack on the citadel of Antwerp in 1832—first, because this was the most regular and scientific siege which had taken place for many years; and secondly, because as a practical operation an account of it must be more interesting and more instructive than any description of the formal theoretical plans which are usually drawn iu the military schools. See Plate XI.

Without entering into any detail of the complicated circumstances out of which the siege arose, in a time of general peace, it may be stated here that Great Britain and France, as joint guarantors of the integrity and independence of Belgium, having failed to procure the evacuation of Antwerp by means of negotiation, were obliged to have recourse to force. Hence the siege is to be viewed as an ejectment executed against the king of Holland, who had refused to renounce possession, unless compelled to do so.

The French army employed to cover and conduct the attack of the citadel of Antwerp in November and December 1832 was placed under the command of Marshal Gerard, and amounted to 66,450 men, viz.:—54,000 infantry, 6000 cavalry, and 6450 engineers, artillery, and pontonniers, with 14,300 horses, and 144 pieces of siege and 78 of field artillery. On the 24th of November Marshal Gerard established his headquarters at the village of Berchem, about 2500 yards from the citadel, and issued orders to commence operations in the evening as soon as it became dark. The garrison of the citadel, under General Baron Chassé, amounted to 4470 men, with 144 pieces of ordnance of all calibres, and abundance of ammunition and stores. It will be observed that a garrison of about 5000 men was opposed to the attack of a besieging army thirteen times its strength.

At eight o’clock p.m. on the 29th November, the French troops destined for this service, consisting of 18 battalions, 900 artillery, and 400 sappers, in all about 17,140 men, assembled at the depots of intrenching tools. The flank companies of these brigades, supported by twelve eight-pounders and a strong piquet of cavalry, formed the covering party under the direction of General Haxo, by whom and the officers of his department (the engineers) the first parallel and approaches were traced out, whilst General Niègre and the officers of artillery marked the sites of the projected batteries. The first parallel leaned on the covered-way of the right face of Montebello, and extended towards Kiel, its nearest point being about 325, and its farthest 435 yards from the advanced front of the citadel. The extent of the first parallel was 1870 yards, and that of the approaches 3750 yards. The communications from the right and centre debouched from the Malines Chaussée, in the village of Berchem, parallel to the road leading from that village to the Harmony and St Laurent; the communication from the left commenced near the garden called Heinrich’s; whilst a fourth, on the extreme right, sprung from the covered-way of the left flank of Montebello, opposite to the first traverse.

On the second night, from 30th November to 1st December, five approaches were puslied on in front of the first parallel,—two in the direction of the capital of the Toledo bastion, two upon that of the Lunette St Laurent, and one, being the fifth, terminating in a place of arms on the extreme left. From the 1st to the 2d December two zig-zags were added to the approaches,—one from the centre, in the direction of the gorge of St Laurent, and the other on the right, diverging towards the curtain, between the Toledo and Fernando bastions. The badness of the weather sadly incommoded the workmen, and prevented the artillery getting the guns into battery. Between the 2d and 3d December four zig-zags were made in front of the approaches on the right and centre, and half a parallel was formed to complete the place of arms constructed on the left during the night of the 30th November. The heads of the zig-zags were advanced to within 135 yards of the glacis. The batteries Nos. 1, 2, 3, 4, 5, 6, and 9 (see Plate XL), with two for mortars in the rear, were armed, and ready to be unmasked at a moment’s notice. The arming of Nos. 7, 8, and 10, on the extreme left, was impeded by the difficulties of the ground. From the 3d to the 4th December, the second parallel was traced and commenced, its right leaning on the foot of the glacis of the counterguard, its centre and right 130 yards distant from the place of arms in the covered-way of the Toledo bastion, and its left towards the right of the covered-way of the St Laurent, at 90 yards from the crest, and 15 from the foot of its glacis. The length of the second parallel was 1250 yards, and with its approaches from the first parallel it occupied 3025 yards of ground. By the greatest exertions batteries Nos. 7, 8, and 10 were armed during the night. This completed the armament, and, at 11 A. Μ. on the 4th, the embrasures were unmasked, and the batteries opened their fire from centre to flanks, and maintained it steadily during the day.

From the 4th to the 5th of December an a pproach was pushed on from the second parallel, directly upon the salient angle of St Laurent, and an entry was made into the covered-way by a return to the left. The garrison discovered this, and opened a sharp fire from the lunette; a lodgment was, however, effected near the spot usually occupied by the first traverse. At this time the garrison suffered much from the fire of the besiegers. From the 5th to the 6th the lodgment made the previous night in the covered-way of the salient place of arms of St Laurent was prolonged as far as the first traverse. But the besieged kept up so vigorous a fire that the French engineers were obliged to renounce the flying and adopt the full sap. The zig-zag in the counterguard, being about three feet in width and four in depth, was conducted along the parapet, nearly to the extremity of the right flank, and within 180 yards of the counterscarp of bastions Toledo and Fernando; and two lodgments, blinded with fascines, were made in the parapet for six guns to enfilade the covered-way of the Toledo bastion. In the meantime a steady fire was kept against Kiel, the ravelin in its rear, aiid the Paciotto .bastion. From the 6th to the 7th a battery of 24-pounders near the village of Burcht on the left and Hoboken on the right opened on the gun-boats which flanked the French post at the Melk Huys. It was intended to assault St Laurent this evening; but as the lunette was found to be well protected by trous-dc-loup, the project was abandoned, and the regular method of descent, passage, and mine determined on.

Between the 7th and 8th of December a shell penetrated the blindage of the laboratory, and, setting fire to the combustibles in it, caused considerable havoc. A battery for six mortars, E, on the right, now opened its fire; another, F, also for six mortars, was traced behind the centre of the parallel; and platforms for four mortars were laid near Montebello. The fire of these batteries ⅛as directed on the Toledo bastion and the buildings within it. On the previous day jets of flame had been seen to issue from the Great Barracks, and, in spite of every exertion, the building was entirely consumed by the evening of the 8th.

From the 9th to the 10th of December the operations against St Laurent were renewed with great activity, and the sap advanced to the crotchet of the second traverse, whilst that intended to debouch upon it from its right was likewise pushed on. The third parallel was opened 130 yards in advance of the second, its right debouching beyond the Boom Chaussée, from the branch running into the covered-way of the counterguard, and its left uniting with the boyau parallel to the foot of the glacis of St Laurent. The garrison suffered much from the vertical fire of the mortars and howitzers, especially the great mortar and the new-model eightinch howitzers. Until the year 1822 the eight-inch howitzer in common use in France measured 3 feet 6 inches French, and weighed 1096 lb, or twenty-three times the weight of the loaded projectile, whilst its calibre was equal to a solid shot of 80 ∏>, and contained 65 ounces of powder. The new-model howitzer was an improvement on the Russian licorne and the Spanish heavy howitzer, perfected by Colonel Paixhans. The raft for the blinded descent into the ditch was brought up to the lodgment, and a second descent à ciel couvert was commenced to the left of the first. The third parallel was improved and widened. A little after dusk on the 10th the besieged made a sortie, which was driven in, but not until damage enough had been done to occupy the French all the night of the 10th and the morning of the 11th in repairing it. From the 11th to the 12th three rafts were got ready, and placed in the descents to the ditch; they were about 12 feet by 8. At dusk the miners returned to the escarp, and, in an excavation made the previous night, fixed two petards, which, by their explosion, produced a fissure in the wall, and a serjeant having immediately entered the hole, commenced a gallery under the centre of one of the arches. At 11 A.Μ. on the 12th the battery H, on the extreme right of the second parallel, opened fire, which, combined with that from the others, told severely on the Toledo bastion. The miners still continued their work under the lunette St Laurent, and commenced chambers for three mines. The fourth parallel was widened during the day.

Between the 12th and 13th of December the minera were at work in the chambers under St Laurent, which were not yet completed. On the right the covered-way of the left face of the Toledo bastion was crowned to within 65 yards. From the 13th to the 14th, after nearly sixteen nights of open trenches, the arrangements for the assault of St Laurent were completed, and orders were issued to prepare for the storm. Too much value was set on this outwork, defended by little more than a hundred men, one five-and∙a-half inch howitzer, two Coehorn mortars, and a six-pounder. The mines being charged, the blinded descent into the ditch was pierced as soon as it became dark, and everything prepared for the assault. Three storming parties of the flank companies of the 65th regiment of the line were posted in readiness, with a column of reserve; and at 5 A. Μ. on the 14th the match was applied to the saucissons of the mines. Three successive explosions took place, and the escarp immediately presented a wide and practicable breach. The fascines for crossing the ditch had been injured by the explosions, but after a little delay the storming party entered almost without opposition, and made'prisoners one lieutenant and forty-eight rank and file, the others having escaped into the citadel. Thus fell the lunette St Laurent.

After this operations were carried on against the citadel, and at 11 A. Μ. of the 21st December the battering in breach commenced, and continued until the 23d. When a practicable breach had been formed, and Marshal Gerard was about to deliver the assault, the garrison surrendered, after a gallant defence, remarkable, however, for its passive rather than for its active character. When Marshal Gerard entered the fortress, General Chassé was found in a casemate in the Alba bastion, which he had occupied during the siege. On their progress from the gate to the governor’s quarters, they passed through a scene of desolation and ruin which baffles description; with the exception of the principal powder magazine, two or three service magazines, and the hospital, not a building remained standing. The terrepleines of the bastions were ploughed into deep ruts by the shells; the gorges were encumbered with heaps of fallen rubbish; and though the casemates and subterranean communications were not perforated, all of them had sustained damage from the incessant explosion of shells, and they emitted an almost insupportable odour, caused by the number of men who had been crowded into them. When Count Gerard took his leave of General Chassé, he observed “that it was high time to surrender, that he had gallantly and honourably done his duty, and that he ought not to have held out a day longer.” With a fortress reduced to a heap of ruins, a garrison exhausted and attenuated, and a breach sufficiently wide to admit a column formed upon a front of a hundred, it would indeed have been madness to attempt to stand an assault

The following is a list of the different batteries, with the direction of their fire respectively :— [table]

. Out of their force of 66,450 men, the French lost during the siege 108 killed and 695 wounded—total, 803. The Dutch had 4937 men in the garrison, of whom they lost 122 killed, 369 wounded, and 70 missing —total 561.

A careful comparison of the details of this siege with the general principles which have been enunciated will enable the reader to recognize the importance of the following maxims :—

1. Independently of the great amount of labour to be provided for in the construction of parallels, approaches, and batteries, there will be a daily drain upon the besieger s forces by casualties, so that he can scarcely expect success unless his original preponderance in numbers has been such as to leave him at the final moment of assault in a condition to attack the diminished garrison with an overwhelming force. In addition, therefore, to a covering army when external relief is threatened or anticipated, the besieging army should be from four to five times the strength of the garrison, or even more, should the nature of the ground add to the ordinary difficulties of approach. This superiority of force is necessary to give celerity ana steadiness to the operations, which would otherwise be tedious and interrupted.

2. A perfect investment is not merely expedient but indispensable. So long as any portion of the enceinte of a fortress is left open the garrison is able to recruit its strength from without, and it is relieved from that moral depression which must oppress men when closed up within a narrow space, and exposed, day after day, to fatigue and danger. Under such circumstances there seems to be no limit to the power of defence, as fresh supplies of men enable the besieged to add intrenchment to intrenchment, and it is only possible to overcome him by determined, reiterated, and overwhelming assaults. Such were the circumstances of Sebastopol; the system of attack forced upon the allies never enabled them to isolate even the southern section of the fortress, and the means of communication between the south and north remaining available fresh troops were continually brought to the south side, and a superiority in numbers given to the defenders over the attacking force. It ought not therefore to be a matter of surprise that the progress of the siege was slow.

3. Good and secure lines of communication are most essential, as there ought to be no interruption after the ground is broken and the siege has commenced. Neither in the attack nor in the defence should guns be fired idly, or from distances and positions from which their fire would be useless or even uncertain; but when the proper distance has been ascertained, battery should succeed battery as the works of approach advance, and no interval for rest or for the repair of injuries should be allowed to the besiegers.

4. The importance of advanced works was well exemplified at the siege of Antwerp, where the whole force of the attack was directed against the advanced lunette St Laurent, whilst the defence, though good, had not the advantage of the collateral defence of the lunette Montebello (see Plate XL). Where the garrison is an army, such works afford the best means for an’obstinate defence, and, by forcing the besieger to act on the circumference of a larger circle, diminish very much his ordinary advantage of concentration.

Siege of Dantzic.

Having thus given an example of an interior and passive defence, we shall now, in further illustration of the principles already laid down, advert to an example of a different kind. The siege of Dantzic, whether considered with reference to the magnitude of the operation, the difficulties to be surmounted by the besiegers, or the active and varied character of the defence, was certainly one of the most memorable events in the campaign of 1807. Before the war of 1806 and 1807 the fortifications had been much neglected, because from the position of the place it was not anticipated that it would have to sustain a siege. But when the battles of Jena and Auerstadt had entailed destruction on the Prussian army, and had laid open the kingdom, General Manstein, who commanded at Dantzic in the absence of Field-marshal Kalkreuth, the titular governor, laboured with much activity in repairing the walls and the palisades, and in completing the enceinte. It is necessary, therefore, to describe the principal defences at the time the place was invested by Marshal Lefebvre, at the head of the tenth corps of the grand army, and before the commencement of the trenches on the lst of April.

The city of Dantzic, traversed by the Mottlau, was surrounded with large ditches filled from that river, the waters of which, retained by several sluices, formed, to the eastward, a vast inundation, which, reaching on one side to the suburbs of Oliva and St Halbrecht, and on the other to the dykes of the Vistula, extended about four leagues, and covered two-thirds of the eastern fronts. On the north the Vistula runs about 260 yards from the covered-way, leaving between the left bank and the glacis of the place an impracticable marsh intersected by canals; at its embouchure, distant nearly three miles, the banks were defended on the right by the fort of Weichselmunde, and on the left by an intrenched camp in the small island of Neufahrwasser, intended to cover and protect the arrival of such succours as might come from the seaward. The ground adjoining the banks of the Vistula being intersected by canals and covered with marshes, was extremely unfavourable to a besieger, as it rendered it difficult for him to form establishments or raise works of proper solidity, and forced him to extend his quarters, disseminate his troops, and multiply his posts. At the period in question this inconvenience was the more severely felt, because the besieging force, though nominally 18,000 strong, was inferior in numbers to that of the garrison, which consisted of 12,000 Prussians and 3 Russian battalions, and it required the most vigilant caution to occupy numerous posts without unduly weakening it. The communication between the place and the fort of Weichselmunde was maintained by a series of redoubts constructed on the borders of the Vistula, and parti cularly by the advantageous position of the isle of Holm, which continued the defence of the place to the fort with the exception of an interval of about 1400 yards, and rendered the communication with Weichselmunde by the canal of Laack secure in spite of any batteries which the besiegers could establish at Schellmühl. The French, therefore, could not attempt to throw a bridge over this part of the Vistula until they had made themselves masters of the isle of Holm. On the west two chains of hills, separated by the valley of Schidlitz, covered the enceinte; and the prolongations of these hills were crowned by the two forts of Bischopsberg and Hagelsberg, which, being connected by intrenchments, formed a second enceinte, leaning upon one side on the inundation of the Mottlau, and upon the other on the left bank of the Vistula. This new enceinte, though constructed of earth and without revetment, was secure against assault, and as the covered-way as well as the foot of the scarps bristled with strong fraises which served instead of revetments, the besiegers had no hope of succeeding by a coup-de-main t and were therefore obliged to proceed by regular attack.

From this description of the defences of Dantzic, it is easy to perceive that the difficulties attending the operation must have been very great·. The principal of these, as stated by General Kirgener, who until the arrival of General Chasseloup directed the attack, were, first, that Marshal Lefebvre had at first an army inferior to that of Marshal Kalkreuth, all of those destined for the siege not having then arrived, and that this army was in a great measure composed of new troops; secondly that, owing to the badness of the roads and the inclemency of the season, the artillery experienced the greatest difficulty in bringing up its convoys, the establishment of the batteries was retarded, and a scarcity of ammunition sometimes prevailed; thirdly, that the place, which could not be completely invested because the approach from seaward was in the hands of the British, required an immense circumvallation, which, in fact, could not be completed until after the arrival of reinforcements; the corps of troops which occupied the quarters were extremely weak, and could neither furnish a sufficient number of workmen, nor even the number of men necessary for guarding the trenches; and fourthly, that the besiegers had no good plan of the place, and did not know the depth of the ditches, and as the accidents of ground in front of the fortifications were extremely diversified, they could only be reconnoitred in proportion as the works advanced. These circumstances, joined to the necessity of concentrating the greater part of the troops close to the camp of Neufahrwasser, by which succours arriving by sea might debouch, and the advantage which the besieged had in retaining the mastery of part of the suburbs, determined the chief engineer, after the investment had been effected, to direct the principal attack against the Hagelsberg, and a false one against the Bischopsberg fort. The true point of attack was the long branch of lines in the plain connected with the bastion on the right of the Hagelsberg: “c’était là le défaut de la cuirasse;” but, for the reasons above stated, approaches were directed against the fort itself.

As the details of this great siege would fill a considerable volume, all that our limits permit is merely to indicate the principal occurrences. On the 1st of February 1807 the troops of General Dombrowski began to approach Dantzic, and took up a position at Mewe, upon the left bank of the Vistula. On the 15th General Menard, commanding the Baden contingent, arrived at the same point, and repulsed a detachment of the garrison of Dantzic, which had advanced from Dirschau to attack him On the 23d General Dombrowski, having been reinforced, received orders to attack a large detachment of the enemy which occupied an advantageous position at Dirschau and its environs. The combat here was obstinate and sanguinary; but the Prussians, though intrenched in a church and a churchyard, were dislodged and driven back, chiefly by the Poles, who, exasperated by their long resistance, put to death without mercy all who fell into their hands. After the combat of Dirschau, General Manstein no longer sought to obstruct the distant approaches. The troops destined to form the besieging army now arrived in succession, and the formation of the park of artillery was commenced. On the 12th of March Marshal Lefebvre found himself in a condition to close in on the place; and the troops of the garrison having withdrawn, he distributed his own in the following positions:—a battalion of French light infantry at Oliva, a Saxon battalion at St Halbrecht in the Burgerfeld, and two at Tiefensee and Kemlade; the Poles occupied Schönfeld, Kowald, and Zunk-endin; some battalions took post at Wonnenberg, Neukau, Schudelkau, and Sniekau; the Saxon cuirassiers and. light horse were stationed at St Halbrecht and Guirsehkens; the 19th regiment of French chasseurs at Burgfeld, and the 23d at Schudelkau; the Baden dragoons and hussars at Wonnenberg, and the Polish lancers at Lan-genfurt. On the 16th the marshal attacked the village of Stolzenberg, which he carried after a warm resistance, as he did also the suburb of Schidlitz, to which the Prussians had retired; and on the 18th the place was invested, with the exception of the eastern part, which, by the isle of Nehrung, communicated with Königsberg. Field-marshal Kalkreuth now arrived in Dantzic, and assumed the command of the place. The next operation of the besiegers was the attack of the isle of Nehrung, which, after a severe and protracted struggle, was carried in the most gallant manner, and measures were immediately taken to secure the possession of this important conquest. A bridge was also established on the Vistula, and various works constructed to check the attempts of the enemy either on the side of Dantzic or on that of Pillau. At this time the governor, who had under his command agarrison of 18,000 men, besides theburgher militia, made a sortie for the purpose of destroying the works of the besiegers; but the attempt failed, and the Prussian columns were compelled to retreat into the place without having obtained the smallest success upon any point.

It had been decided that the principal attack should be directed against the fort of Hagelsberg (because the redoubt of Bischopsberg was more complete and better flanked by the fire of the place), favoured by two false attacks, the one directed against the intrenched camp at Neufahrwasser, and the other against Bischopsberg, and by two secondary attacks on the left bank of the river; and ground was broken on the night of the 1st and 2d April, at the distance of 1600 yards from the palisades. The approaches were pushed forward with the greatest vigour, and on the night of the 11th the second parallel was commenced by flying sap. On the morning of the 12th the batteries were armed. On the 13th the enemy made a sortie in force, attacked the Saxons with great impetuosity, carried a redoubt constructed upon the mamelon of Hagelsberg, and penetrated even to the head of the trenches; but they were ultimately repulsed, though not without difficulty and loss. By the 23d all the batteries of the first and second parallels, and those of Stolzenberg, were armed, and emplacements were provided for field howitzers, from which to throw shells into all quarters of the city. At daybreak on the 23d the batteries were unmasked, and, though the garrison returned the fire with the greatest vivacity, by the 24th the besiegers, firing with 56 heavy guns, had obtained the ascendency, committing great ravages in the place. Being apprised of this circumstance, Marshal Lefebvre summoned the governor, who replied in a manner worthy of himself. The fire of the mortar and reverse batteries continued during the 25th, in the course of which a new battery was constructed between the low flanks of the Stolzenberg, and the direction of some others changed, in order to batter the right bastion of Bischopsberg, the fire of which had greatly incommoded the French batteries. During the day of the 26th the fire on both sides was exceedingly animated; but at seven in the evening, that of the garrison suddenly ceased, and a column of 600 Prussian grenadiers, followed by 200 workmen, sallied out of the place. As tïae sortie had been foreseen, preparations had been made to repulse it. It was attacked in front and on both flanks; the whole column was either killed or token prisoners. Meanwhile the works were vigorously pushed forward at all points. The batteries of Stolzenberg were united with the attack on the Bischopsberg; emplacements were prepared for batteries à ricochet; at the attack of the lower Vistula the works were continued, and a tongue of land situated at the extremity of the isle of Holm token possession of and isolated by means of a cut, whilst at the principal attack the greatest exertions were made to prolong the right of the third parallel, and enlarge the communications. On the 30th April the batteries of the besiegers, augmented by several pieces which had arrived from Warsaw, thundered on the place, in different quarters of which conflagrations appeared; and the besieged replied by the fire of all the batteries of the front attacked, directing more than thirty pieces on a redoubt which fired with the greatest effect But as the fire of the besiegers had made little impression on the exterior fortifications, which were of earth, it was during the first days of May directed chiefly against the palisades, and the utmost activity was at the same time evinced in extending, improving, and urging forward the attack; whilst, on the other hand, the garrison showed equal vigour in obstructing the approaches and destroying the works of the besiegers. In fact, notwithstanding the address of the French artillery, that of the garrison still remained effective, because it had not been possible to ricochet the lines of the fortifications, and the resources of the besieged in munitions of all kinds were more considerable than those of the besiegers.

On the urgent recommendation of General Chasseloup, who had by this time assumed the direction of the attack, it was decided that the isle of Holm should be assaulted, as the possession of it would enable the besiegers to take in reverse the front attacked. The besieged had spared no pains for the preservation of this important post, from a redoubt on which, called Kalke Schauze, they had continually annoyed the left flank of the trenches. In the night of the 6th and 7th of May, however, it was attacked, and carried after a desperate resistance, whilst the possession of it was secured by works added to the intrenchments which had just been stormed, and its batteries were turned against the place. At the principal attack the fire of the besiegers had also mastered that of the besieged; and Marshal Lefebvre was preparing to assault the fort of Hagelsberg, when on the 12th a Russian corps d’armee of 18,000 men, under the command of General Kamβnskoi arrived by sea, and disembarked at the intrenched camp of Neufahrwasser.

At the moment of landing his troops, General Kamenskoi was ignorant of the capture of the isle of Holm, and he was disconcerted to find such an obstacle to his communications with the place. This occasioned delay which proved fatal to his enterprise; for had he attacked immediately on landing, it is not improbable that he would have succeeded. It was only on the 15th of May, however, the third day after the disembarkation, that he made an attempt to succour the besieged city. He began to debouch at four in the morning, and, under cover of a brisk cannonade, formed his force, consisting of 12,000 men, in four columns of attack. The onset was impetuous, and at first the Russians gained ground; but they were ultimately repulsed at all points, and forced to retreat with great loss to the intrenched camp. Field-marshal Kalkreuth made no attempt to second this attack by a general sortie, which would have placed the French between two fires; and by its failure the fate of Dantzic was decided.

The works of the besiegers were now pushed forward with redoubled vigour; and the following day preparations were made for the assault of Hagelsberg. Foreseeing this, Marshal Kalkreuth resolved to make a last effort to destroy the nearest works of the besiegers, and for this purpose ordered a grand sortie, which took place on the evening of the 20th May; but although the Prussians fought with all the fury of despair, they were driven back, and pursued into the ditch of the place. On the 21st the besieging army was reinforced by the arrival of the troops of Marshal Mortier, part of which had remained before Colberg; the marshal himself quickly followed; and orders were immediately issued for the assault of Hagelsberg. Before giving the signal, however, Marshal Lefebvre again summoned the governor of Dantzic, who, having no longer hope of succour, and being convinced that the besiegers were in a condition to make themselves masters of the fort of Hagelsberg, showed a disposition to capitulate. A suspension of arms was accordingly agreed to, and this was followed, on the 24th of May, by a capitulation, the principal conditions of which were similar to those which the field-marshal himself had granted to the garrison of Mayence in 1793.

These two sieges illustrate so well the principles of attack and defence, and are so perfect of their kind, that it has not been thought worth while to add an example of a more recent siege; but it should be observed that in future the preliminary operations of the besieger must take place at far greater distances; he will break ground for his first parallel at not less than twice the distance hitherto laid down, and will place his first batteries in rear of the parallel. This, while entailing on him much greater labour in parallels, trenches, and approaches, offers counterbalancing advantages, as it allows him to disperse his batteries in small units without the sacrifice of any of their power of simultaneous concentration on the point of attack, and with diminished exposure to the counterblows of the enemy’s artillery.

Bastioned Systems of the Netherlands.

The Bastioned System of the Italians was carried into other countries by their engineers, who were extensively engaged in the service of foreign princes, and the celebrated Italian engineer Marchi, coming to Brussels with Margaret of Austria in 1559, appears†o have introduced the Bastioned System into the Netherlands. It has been shown that in permanent defences, the ordinary earthen scarp adopted in ditches of field works had been replaced by a masonry revetment as a security against surprise, in consequence of which, in old Italian fortresses, lofty revetments were almost universal; but in a country the soil of which is permeated by water within a few feet of the surface, such a mode of guarding against escalade would have been enormously expensive, and the alternative was adopted of forming broad wet ditches round the ramparts, and by thus securing them from sudden attack, revetment became unnecessary. The first example of a fortress surrounded by simple earthen ramparts without revetments is said to be that of Breda, fortified in 1553 by Count Henry of Nassau, and this arrangement required only to be moulded into the bastioned trace to constitute the ancient system of the Netherlands, as described by Freitag in 1630. Freitag made the flanks of his bastions perpendicular to the curtain, the faces 98 yards long, with a flanked angle not exceeding 90°, and the length of the curtain 149 yards.

Freitag had strange notions respecting his profiles, regulating the height and thickness of his ramparts not so much by the resistance they were required to offer to artillery as by the number of sides of his polygon; but disregarding these vagaries of the systematist, the annexed cut (fig. 68)

may be assumed to represent the profile usually adopted by the Dutch engineers, R being the body of the place, F the fausse-braye, D the ditch.

It will be observed that the main rampart is surrounded by an advanced parapet called a fausse-braye. This advanced parapet was intended to deliver a grazing fire on the ditch, whilst the space between it and the rampart formed a spacious chemin des rondes for the assemblage and movement of troops"; but great as these [advantages are, the fausse-braye has dropped into disuse. It is not possible to remain in it under a heavy vertical fire, the shells either dropping directly, or rolling down into it from the slope of the rampart above. Such shell traps, as they are called, are scrupulously avoided by modern engineers, who know that the improvement of vertical fire will ere long add materially to the difficulties of defence. In the bombardment of Sweaborg, an illustration was afforded of what may be expected of heavy mortars, when the shell becomes a better representative of a mine than it now is. At present a 13-inch shell weighs, when loaded, 200 pounds, and can carry a charge of 11 lb of powder, which is ample for breaking the shell and scattering its fragments, but is insufficient for producing the effects of a mine.

The Dutch System of Coehorn deserves especial attention, and is represented in Plate IV., fig. 1, which exhibits his first system. The great characteristic in this system is the combination of wet and dry ditches, and the use of covering works, or couvre-faces, intended to preserve the body of the place from injury till an advanced period of the siege. These envelopes were first proposed by Dürer, and it is worthy of note that the remarkable orillon of Coehorn is a reproduction on a modern scale of the complicated casemated structure of one of Dürer’s basteien. Coehorn was well acquainted with the principles and the systems of the eminent German engineer Speckle, and adopted them when applicable to his purpose. The profile (fig. 69) may enable the student to appreciate the difference between the dry ditches of Coehorn and the narrow passage afforded by the fausse-braye of the older engineers.

The profile exhibits also the loopholed galleries of the counterscarp, by which a reverse musketry fire is directed on the revetted escarp of the inner rampart,—a system of defence which has since been generally adopted, and is most valuable when a secure communication can be kept up between the galleries and the work which they are intended to ^defend. After the great siege of Corfu by the Turks, and its successful defence by Schullemburg, some Dutch engineers who had been invited to Corfu by him, and had taken part in the defence, were employed in adding detached forts to the old Italian bastioned fronts. In these works the ruins of'numerous examples of loopholed galleries and loopholed traverses may be observed; and they demonstrate that though Coehorn adopted in his writings his reliefs to the aquatic sites of Holland, he developed principles of defence which were equally applicable to other sites and other countries. It has been argued by Bousmard and others that an opening would be formed by shells through the couvre-face, and that the flanks of the bastions would be thereby exposed to the fire of the counter batteries on the glacis; but it remains to be proved whether such an opening through an earthen mass could really be effected by the horizontal fire of shells; and the French translator of Zastrow, Μ. Neuens, captain of artillery, justly remarks that, “if shells fired horizontally into earthen works are so efficacious in destroying them, such shells must be a still more powerful instrument in the hands of the defenders for destroying the besiegers’ batteries.” Zastrow observes that, if we admit with Coehorn and others that, though the besieger may succeed in destroying a few feet of the parapet of the lower or outer face of the bastion, he would in vain, by firing shells horizontally into its mass, endeavour to lay open the counterscarp galleries, it must be admitted that he would, on mounting the low face, find himself in a most critical position, as all the defences, both direct and reverse, of the dry ditch, would remain uninjured, and be in full action against him. These dry or inner ditches, which facilitate the war of sorties, and the reverse or counterscarp galleries, are defensive arrangements of great merit, and may, by modification of profile, be adapted to any site; though the advantage dry ditches offer in such countries as Holland, where the besiegers cannot excavate in them without coming to water, cannot be expected in other sites, and must be made up for by stone pavements, or other contrivances likely to embarrass the besieger in his excavation.

Coehom assumes the plane of site to be 4 feet above the level of the water, and the dry ditch of his bastion is at its centre on the level of the water, so that a passage by sap becomes impossible, as the spade sinks at once into water; but near the escarp and counterscarp the ditches are 2¾ feet below the plane of site sloping on each side towards the central portion. The breadth of the dry ditch of the bastion is 98 feet, and that of the wet ditch before the salient 148 feet. All the slopes are at an angle of 45°. The whole breadth or thickness of the couvre-face, measured at the water level, is 52 feet, so as not to afford space for the besiegers’ batteries, and its relief of construction only 12¾ feet. In the ravelin the relief of the low face is 10 feet, of the high face 18¾ feet, and the height of its revetment 8 feet; in this work also the thickness of the low face would not afford space for batteries. The width of the dry ditch is the same as that of the bastion. These few details, with an examination of Plate IV., and of woodcut 69, will enable the student to comprehend the general principles of this great engineer; and it is rather by tracing out the ideas of a master mind, as exhibited in the peculiarities of his plans, than by studying the plans themselves as wsholes, that the engineer will acquire practical knowledge which will enable him to vary his own projects, so that they may really be the best suited for the ground he is working upon.

Coehorn never restricted himself to the rules even of his own system. In fortifying!Gröningen he was required to construct works on an eminence which commanded the town and he adopted a trace towards the exterior of tenailles, the gorges of which were closed by small bastioned fronts constructed by walls which should be easily breached from the main works when the enemy had succeeded in gaining possession of any one of the intervening redans. By this curious combination of the tenaille and bastioned systems, Coehorn gave an undoubted proof of his superiority to the narrow prejudices which often prevent the adoption of the system best suited for the place.

Methods of Bousmard, Carnot, Chasseloup, Dufour, Noizet, Haxo, and Choumara.

It would be wrong to dismiss the subject of Bastioned Systems without at least some more reference to the works of these distinguished engineers than has been given in tracing the history of this subject. Bousmard makes the faces of his bastions as well as their flanks curvilinear, the former convex, and the latter concave outwards; but though by this arrangement the effect of ricochet fire may be diminished, the difficulty of defending the salient from the flanks is much increased. His great innovation, however, consisted in placing the ravelin and its redoubt in advance of the glacis of the body of the place, and forming in front of them a second or advanced covered-way, the object being to close the main ditch entirely, so that the besiegers’ batteries should not he able to fire upon the body of the place through the ditch of the ravelin. The covered-way is made en cremaillére, and at each bend there is a sort of redoubt, or casemated traverse, not a simple hollow traverse loopholed, such as those in the detached works of Corfu. It has been objected to Bousmard’s system that his advanced works would be speedily taken by turning the gorges both of the ravelin and its redoubt, but it should be remembered that the interior slope of both is replaced by a loopholed wall, being the front of an arched gallery running all round, so that the enemy could not remain within these works exposed to the fire from the galleries, as well as from the body of the place. Without advocating the precise form and disposition of the works recommended by Bousmard, it may be reasonably asserted that in every case of a powerful and well-appointed garrison, the defence will gain by assuming an active character beyond the precincts of the glacis.

As already observed, an unmerited indifference has been manifested by many engineers to the merits of Carnot, principally, it may be believed, from his exaggerated estimate of the effects of a vertical fire of small projectiles. Although he appealed to imagination rather than to calculation, when he assumed that by substituting 600 wrought iron balls, weighing each ¾ ft, for the one shell of 150 ft, with 6 mortars projecting 3600 balls, he might expect to put hors de combat 20 men at each discharge, or 2000 in 100 discharges, he was right in urging the importance of vertical fire. Carnot constructed his escarp without a revetment, but placed a detached loopholed wall in frontof it with a chemin des rondes between, which is one essential feature of his system, the wall being constructed with arched niches in rear so as to shelter the men defending it; the loopholes are in two rows. He provided arched casemates for mortars on the gorge of his bastion in order to fire upon the capital, and the loopholed wall of an inner curtain, being continued along the retired flanks and in front of these mortar casemates, formed a complete inner retrenchment. Between the tenaille and the ravelin was an earthen cavalier, occupying the position of a redoubt in the ravelin, before the bastion’s counterguard, so that the whole of the interior works were masked by these earthen envelopes. There is much ingenuity in these arrangements, and at least as full an appreciation of the value of earthen works as can be found in the writings of any modern writer. Carnot’s leading principle, however, was, that a successful defence must depend on the active operations of the garrison, and that sorties therefore should be frequent and determined as soon as the enemy had approached close to the fortress. For this purpose he removed the revetment from the counterscarp, and formed it into an easy or countersloping glacis, to admit of the ready advance of the troops from the ditch upon the head of the besiegers’ sap. He supposed that the overwhelming vertical fire of the 10 mortars in the mortar batteries in the gorges of his bastions would prevent the enemy from accumulating large covering parties in the trenches, and that he should therefore be able to fall upon the working parties and successfully delay the progress of the works. It has been shown that Carnot entertained an exaggerated view of the effects of vertical fire, but the idea of securing his mortars in casemated buildingsis good, and has been adopted in the citadel of Ghent, and in several English works at Portsmouth and Plymouth; and it is impossible to study his works without profit.

Chasseloup (1754-1835), like Bousmard, placed his ravelin in advance of the glacis, and provided it with a small casemated keep, the flanks of which are pierced for two guns each. The tenaille is also provided with casemated flanks, and in front of it is a casemated redoubt or bastionette to supply the place of the ordinary ravelin, and to flank the salient portion of the face of the bastion, the general face being by him bent into two, so as to place the salient portion in line with the exterior side of the polygon, and thereby secure it from the ricochet fire. Casemated redoubts in the re-entering and salient places of arms, a defensive barrack, and a permanent entrenchment on the bastion are also included in his arrangements. De Sellon (Memorial de L’Ingénieur Militaire) observes, “It would indeed be well to force the besieger to pass through two sieges, if the outworks pushed so far forward] had higher scarps, and were not so easily turned at the gorge, but as the scarp is only 13 feet high, this possibility of attacking the works by the gorge without a previous descent into the ditch presents such serious inconveniences that it is surprising to observe that Bousmard and Chasseloup should have adopted so defective an arrangement.” But notwithstanding this strong condemnation, it is at least doubtful whether such works are not the most suitable for a vigorous defence by a strong garrison, as they would enable the besieged to fall upon the assailants at the most critical moment of their attack with a powerful force; and it may be added that a skilful engineer would know how to throw many difficulties in the way of turning these advanced works, whilst the continuance of the besiegers in them might be rendered both difficult and dangerous in the extreme.

The most remarkable feature in Dufour’s modification of the modern system is, that one face of the redoubt in the re-entering place of arms is carried across the ditch, and connected with the coupure of the ravelin, so as completely to close the ditch and cover the face of the bastion from the fire of a battery on the glacis of the salient of the ravelin. Dufour also raised the salient of the ravelin into a high cavalier, so as to secure the faces from ricochet; and he proposed that the cavalier should be formed of gravel or small stones, so that the fire from the body of the place might, by scattering about these natural missiles, cause great damage to the enemy, when attempting to form a lodgment.

General Noizet has been already mentioned in connexion with the Modern System, his modification of which is now the normal system adopted at the French military schools. Rejecting Dufour’s mode of closing the ditch of the ravelin by carrying across it one face of the redoubt of the re-entering place of arms, he effected] the same object by placing"a massive mask between the coupure of the ravelin and the re-entering place of arms, from the inner escarp of which it is separated by a passage. The counterscarp of the bastion is carried continuously along the inner edge of the mask, whilst in front of it is a ditch which separates it from a demi-caponnière forming its counterscarp and covered-way, and a glacis sloping down the ravelin of the ditch. The mask, the lunette redoubt in the ravelin, and the redoubt in the re-entering place of arms form a combined series of works of great efficiency for defence, which completely cover all but the salient portion of the face of the bastion. The flank of the bastion, as before observed, forms an angle of 80" with the line of defence, and the advantage taken of this in the citadel of Ghent in forming a most powerful intrenchment in the bastion, with a curtain as long as that of the main front, has also been pointed out.

General Haxo, one of the ablest engineers of modern times, did not publish his scheme of defence, nor did he reproduce it as a whole in the works he constructed, doubt less considering, as has been so frequently urged, that systems, so-called, can only be looked upon as the exhibition of great principles, not as rigid rules for their application. His ravelin is made very prominent, and the salient is formed into a traverse, or mask, casemated and armed with artillery. Within the ravelin there is a redoubt, and within that a casemated caponnière or bastionette. The ditch of the ravelin is closed by continuing the counterscarp across it with a glacis slope into the ravelin ditch, and by this arrangement the ditch of the redoubt in the ravelin is also closed. The counterguards, the higher and the lower bastions, form almost three lines of defence, of which two, the outer and inner, are powerfully armed with artillery. The peculiar characteristic of the system is, that the parapet is thrown back, and made in its trace independent of the escarp, so that, whilst the latter retains the usual straight line, the parapet is broken into several portions not in the same line, and thus secured from the effects of ricochet— an arrangement of very great merit, and largely adopted in the Polygonal system. Haxo is probably better known to English engineers as the inventor of casemated batteries à l'IIaxo than from his merits as an engineer, great as they were. These batteries are formed in the parapet, and though arched over with masonry, are covered with earth. They are open in the rear to the terrepleine, and the openings in front for the guns are continued into embrasures formed in an extension of the parapet at these points beyond its ordinary retired position in Haxo’s system. These batteries are thus secured from the effects of the enemy’s fire, and when the embrasures are masked are equally hidden from his view, so that they may at any moment suddenly open a powerful and unexpected fire upon the besiegers. Being open in the rear, and connected together by arched openings between every pair, the circulation of air is sufficient to do away with the inconvenience from smoke, so generally complained of in casemated batteries. The batteries à ΓHaxo have been used at Grenoble and Lyons, in the forts of Loyasse and Sainte-Foy, and in many English works. Their value has been much diminished by the range, penetration, and accuracy of modern rifled artillery.

The work of the commandant of engineers, Μ. Choumara, entitled Mémoires sur la Fortification, was published in 1847. In this treatise he maintains the principle that the direction of the parapet should be independent of that of the escarp, the latter being formed in straight lines, and considered permanent during the siege, whilst the former may be broken into several lines, and may be modified during the siege so as to facilitate the defence in any direction. Haxo had in his lessons or studies pointed out the importance of this principle, but Choumara was the first to advocate it in print. The castle of Naples exhibits an early example of the reverse operation, a new escarp having been built in front of the ancient round tower forts, so as to change them at the base only into bastions, whilst the upper portion of the towers became retired and independent parapets. Choumara, not relying on the bent trace of his retired parapet as a security from ricochet, proposed a traverse on the capital of his bastion, placed outside of the retired parapet, and 33 yards in length. This traverse, made 26 feet high and 78 feet wide at its base, would occupy less than two-thirds of the space of the twelve ordinary traverses required to secure from enfilade the faces of Choumara’s bastions 164 yards in length, whilst it would cover not only the bastions but the flanks also. In addition to the traverse or mask on the capital, Choumara proposed high traverses, parallel to the flanks, at about 22 yards from the salients, which would not only secure the faces from enfilade, but would form secure or interior flanks, as cavalier flanks, commanding and firing over those in front. By making the cavalier flanks 98 yards long, and casemating them à VHaxo i 15 guns might be placed in each, and the covered-way of the bastion attacked would be commanded by 30 guns in addition to those of the ordinary flanks, whilst the traverse of the capital would secure the flank cavaliers from ricochet. The last and most remarkable suggestion of Choumara is the proposal to widen his ditch to about 50 yards, and leaving a passage of communication of 16 yards round the base of the escarp, to form an interior glacis, sloping up from the base of the counterscarp towards the summit of the escarp, and having a base of 34 yards wide, thus constituting a continuous mask round the escarp. In respect to countermines, Choumara proposed to replace the great galleries, which are usually made 6 feet high and 3 feet wide, and which are the great arteries of a system of mines, by large vaulted galleries from 16 to 20 feet wide, pierced through the counterscarp, and continued as far as the third parallel. Six of these galleries were to be formed in each front, being placed about 55 yards apart, and connected together by minor transverse galleries or branches. Galleries of this magnitude would, in time of peace, be useful as stores, and in time of war would greatly facilitate the operations of the miner.

The details of military mining cannot be discussed here; but it may be stated that this subterranean warfare requires great skill on the part of both besieged and besieger. The besieged has the advantage of having had the main galleries of his countermines formed beforehand, but in spite of this a war of mines must generally be in favour of a besieger, since every explosion of the mines of the besieged, however destructive it may prove to the assailants, must destroy some portion of the works of defence, whilst every explosion of the besieger’s mines must operate upon his enemy only. Starting, however, upon the assumption that a fortress, except in situations which renders regular attack impossible, must ultimately fall, the real object of defence is to occupy the enemy for at least the time for which the fortress was designed to resist; and the destruction of the lodgment or of the battery of a besieger may materially protract the resistance of the intrenchment formed in a bastion, and thus enable the besieger to maintain his ground the longer.

The most simple forai of mine, and that which may be most readily applied as an obstacle in the .way of the assailant, is the fougasse. It consists of a chamber placed at the bottom of a pit about 12 feet deep. The charge is placed in a wooden box, and both the charge and size of the box may be thus estimated. When the line of least resistance, or shortest line drawn from the centre of the charge to the surface of the earth, which in this case is the depth of the pit, is 10 feet, a charge of 100 lb will produce an entonnoir or excavation, the radius of which is equal to the line of least resistance; and it has been ascertained that the volume of the excavation varies with the charge, the line of resistance and the resisting medium being the same, and that the volume varies also as the cubes of the lines of least resistance; hence, therefore, if W represent the weight of the charge, B the bulk of the entonnoir corresponding to 100 ft of powder and a line of resistance equal to 10 feet, and b that of the entonnoir corresponding to the charge W and the line of least resistance R, we have 100: W:: B: b ; but as B: b :: 10 3 : R 3 , we have 100: W:: 10 3 : R 3 , and W=jθ R 3 . Now let S = side of cubical box to contain the charge (55 ft of powder thrown

√R 3

ÏÕ×55 = 0 ft’ or nearly ⅜ R in feet. The pits for fougasses vary generally from 8 to 12 feet in depth, and· from 3 to 4 feet in width, being made square, and are revetted with planks when the earth is not firm enough to stand without support; and for this latter purpose gabions may be used of different diameters, so that the smaller may be slipped through the larger, which have been previously fixed. The box for the powder is well tarred, and when intended to be left in the ground for some time, it should be covered with tarred canvas and put into another box, also tarred both inside and outside. The charge is ignited by Bickford’s fuze, or by a saucisson or linen tube about an inch in diameter, filled with powder, and enclosed in a wooden case well tarred. The saucisson and its covering should be laid in a trench, sunk some feet in the earth, from the charge and pit to the place of ignition, in order to secure it from accidents as well as from the enemy’s observation (see fig. 26, page 429, in which is also represented the mode whereby the fire is applied by what may be called the fire-box, the end of the trough and powder-hose being introduced into it). As for the thorough fulfilment of the object of a military mine the explosion should be “immediate,” it is requisite to employ a contrivance for producing instantaneous ignition. This can be most readily and perfectly effected by employing electricity, and this is now as a rule employed in regular mining operations.

Experience has shown how little real injury the explosion of fougasses do to an assailant; but, as the moral effect of them is a degree of hesitation or irresolution often greater than that produced by musketry fire, and as they are easily extemporized, the fougasse may still be considered an obstacle of some value to the defence. Loaded shells packed in a case may be substituted for the ordinary charge, the case being formed with a horizontal partition, and the fuses of the shells placed on the lower portion of the case, passing through holes in the partition, so as to be brought into connection with the firing-hose in the upper portion of the case. Another form is the stone fougasse, which is probably the most effectual of all. It is constructed thus. A conical pit is made in the earth about 5 or 6 feet deep, the axis being directed towards the enemy at an angle of 45° with the plane of construction, and at the bottom a charge of 50 lb of powder is placed in a well-tarred box. Over the box, and perpendicular to the axis of the cone, is fixed a lid, on which as a platform are packed either stones or broken bricks, which, on explosion, are scattered over a space of about 60 by 70 yards. It should belaid down as a rule that facilities for discharging mines ought to be in every fortress, whether electric apparatus be used for the purpose, or openings be prepared in the works through which the powder-hose may be carried.

The last great modification proposed by Choumara is the extension of the exterior side, and the value of this can no longer be matter of doubt, now that the effective range of musketry has so much increased. The length of the line of defence may now be safely and advantageously fixed at between 400 and 600 yards, so that musketry and artillery can co-operate together efficiently. Chasseloup had, indeed, proposed to make his exterior side about 700 yards long, and he was no mere speculative engineer, for he had fortified with great skill Alessandria in Piedmont; but it must be borne in mind that no greater distance should be allowed for musketry than is compatible with distinct vision and a correct appreciation of distance; and further that the men intended to use the rifle in a fortress ought to be well trained for that object. The Gatling gun may in fitting positions be used with effect instead of musketry; it delivers a continuous stream of bullets at the rate of 400 per minute. The value of one Gatling is equal to 22 rifles, and nearly equal to two 9-pounders, and though it has a range of 1200 yards, it produces its best effect at short distances. In the defence of ditches its defect is that it cannot break or overturn scaling ladders.

German System of Defence. ¼ Having traced the history of bastioned defence to the high state of perfection it attained, a summary of other systems will complete the subject. It has been shown that no sooner had the Italians invented the Bastioned System of defence than it found in every country persons who devoted themselves to the improvement of its details, —in France, Errard, Pagan, and Vauban; in the Netherlands, Freitag and Coehorn; and in Germany, Speckle, who was at least equal to any of the others. Germany however justly it prided itself on Speckle, has gone back to Dürer, and has adopted from him the system of flanking defence, which depends on casemated galleries, and caponnières or casemated works placed across the ditches. Yet, notwithstanding this, it is remarkable that the Germans have taken much of their works from a French officer —the celebrated Marc René, Marquis de Montalembert, who in 1776 published his celebrated work, Perpendicular Fortification, or an Essay on Several Methods of Fortifying a straight line, a triangle, a square, and all polygons of any number of sides, giving to their defence a perpendicular direction; also, Methods of improving Existing Defences and rendering them much stronger; also, Redoubts, Forts, and Field Intrenchments, of a New Construction, in 11 quarto volumes, with 165 large plates,—a work which must be considered the source from which all the modern “inventions” in this branch of Fortification have been derived. Referring back to earlier German writers, it appears that Rimpler in 1673 proposed a system which is a combination of bastions with tenailles, and that Landsberg in 1712 proposed a purely tenaille system; but both these adhere to earthen ramparts and parapets, the first with revetments, the second without them, and their systems are little more than extensions of Field Fortification. But Montalembert, in his Tenaille System, replaces the simple revetment at the re-entering angles with casemated works in two stages, thus affording direct fire, both of artillery and musketry, for the defence of the ditches and faces of the redans, the remaining portion of the trace being occupied by an earthen couvre-face work, with a detached loopholed gallery in front of it, evidently the prototype of Carnot’s detached revetment. The re-entering casemates are calculated to hold 24 guns in two tiers. Behind the couvre-face is the body of the place of the redan, being also fronted by a casemated gallery, and separated from the couvre-face by an inner wet-ditch. In this system, then, the defence by musketry as well as by artillery is from two levels, the upper at a moderate height above the bottom of the ditch, and not, as in the old Italian systems, at the high level of the crest of the parapet. At the gorge of each redan is placed a formidable casemated tower; whilst in front of the main ditch there is a general couvre-face provided with casemated galleries, a second or advanced ditch, places of arms in front of the re-entering angles, a coveredway, and a glacis.

The Polygonal System may, however, be considered as springing directly from Dürer’s work of the same name, only in this system the simple earthen ramparts of Dürer are replaced by a combination of casemated towers, casemated galleries, and earthen couvre faces. In Dürer’s polygon the sides were straight or unbroken, but in Montalembert’s the centre was thrown back and formed into an Italian bastioned trace, the faces flanking the faces of the caponnière. In forts which formed a triangle or square Montalembert was rich in resources, though the massive casemated tower, casemated galleries, and earthen couvre-faces were the essential elements of all. Tn France, the views of Montalembert have never been received with enthusiasm, though Cherbourg is fortified in conformity to them, and it was even alleged that the corps du genie was indisposed to receive instruction from an officer of another arm; but it is more reasonable to suppose that the cherished name of Vauban has induced its officers to direct their attention rather to the improvement of the Bastioned System, which they have certainly carried to perfection, than to the development of a system depending on such different principles. In Germany, on the contrary, Speckle is less known than Vauban, and though probably a thought of Dürer may not have entered into the question, Montalembert’s Systems, founded upon some of Dürer’s principles, have been adopted, and may be studied in the works of defence of Coblentz. In all such works masonry defences or casemated buildings assume a character of the highest importance, but it should not be forgotten that masonry can never resist the effects of a concentrated fire of heavy guns, and can be considered safe only when protected by earthen masks or couvre-faces. The Maximilian towers of the defences of Lintz are no longer approved by modern engineers, and in closing the harbour of Sebastopol against approach by sinking a large portion of their own fleet, the Russians exhibited their distrust of masonry defences when opposed to ships. And this distrust is not to be wondered at, when it is remembered that, to bring the guns forward enough to afford them lateral training, the walls of casemated batteries must be cut into, and greatly weakened. This great defect of masonry defences, and the evils of smoke in close casemates, are well known to engineers. In the earliest periods of Italian fortification, the necessity’ of increasing the active power of the flanks beyond that afforded by their length was strongly felt; and retired flanks, rising one above the other, were adopted, as well as casemated flanks admitting two or more tiers of guns, thus obtaining, as in Montalembert’s System, a greater number of guns by extending the battery vertically. At first sight this appears an obvious mode of acquiring a superiority over the attack, in which the batteries can only be extended laterally, but in practice the retired flanks were soon found to be untenable, while the front flanks were complete shell-traps, and the casemates were practically useless from the difficulty of clearing the smoke from them. The systems of Montalembert partake of the same defects; and however imposing the appearance of several successive tiers of guns may be, it should be remembered that, covered by a mask, they can only be partially used when the enemy is at a considerable distance, and that exposed to view they can be easily destroyed at 2500 yards by the guns of attack of the calibres now in use. Several writers have proposed systems based upon principles similar to those of Montalembert, but it is perhaps sufficient here to mention the work of Don Jose Herrera Garcia (Teoria AnaLytica de la Fortificacion Permanente), as it is unquestionably the most remarkable development of the tower system of defence. Garcia proposes several successive lines of massive casemated buildings or towers, of an egg-shape, connected together with casemated curtains. The towers are surmounted by parapets, which at the ends next the enemy are broken into a series of smaller curves, and are retired or independent of the exterior wall or scarp. As each of these towers is defensible of itself, the work of forcing a way through three lines of them would be most formidable, but the expense of such a system would h>e enormous.

The system of the Swedish general Virgin belongs to the bastioned systems, but it is mentioned here in contrast to Garcia’s, as it disperses in the defences separate bastioned forts,—of a form somewhat approaching to Rimpler’s, and covered by outworks so arranged as to secure the inner works from injury until the enemy has effected his lodgment upon them. These forts are surrounded on all sides by ditches, and connected together by secure communications. Ingenious as Virgin’s system is, it is manifest that though the loss of one fort would not ensure the fall of the others, it would at least render all the interior space inclosed by the line of forts untenable, and place the town, the arsenal, or other public buildings, at the mercy of the besiegers. This may be said of all detached forts, and it must be again laid down as a maxim that the ultimate value of such forts, as a means of securing an important object, depends on an inner line of defence of a nature to resist any sudden attack or coup-de-main. Detached forts may be, for the purpose of keeping an enemy at a distance, more effectual than a simple continuous line, but they cease to be of use if an enemy can pass them and attack a defective interior line behind, incapable of resisting a coup-de-main.

It has been well stated by the French translator of Zastrow, that the reduction of a place may be considered as a certain amount of work to be performed, the magnitude of which depends on various elements, amongst which the disposition and nature of the works constitute the most important; and that the attack has to perform this work in a certain time, and with certains means, amongst which the principal elements are the quantity of heavy artillery, and the nature of the ground over which the approaches must be carried. When, therefore, it is said that a work fortified on Vauban’s first system would fall on the twentyeighth day,—on Cormontaigne’s, with a cavalier entrenchment in the bastion, on the thirty-first,—it must be remembered that this implies the possibility of complete investment, and of steadily advancing the approaches over soil easily worked by the sapper; but that if the investment be incomplete, if the ground be rocky, and every inch have to be gained by hard and incessant toil, protracting the time during which the sapper is uncovered, and therefore greatly adding to the daily losses in the trenches, such periods may readily be extended to twice or three times their ordinary length.

Intrenched Camps.

It would not be proper to leave the subject without a brief description of intrenched camps, especially as they have an important bearing upon the defence of capitals, with which this article closes.

An intrenched camp is a position, prepared beforehand, in which an inferior army rests in security from the attack of a superior army, and from which it may operate upon the communications of such superior army, or in which a beaten army takes refuge for the purpose of reorganization. The position selected for an intrenched camp is usually around the capital, or around an important city, or on an important line of communication. The position should, therefore, contain suffi cient space to receive the army for which it is constructed, to contain ample supplies of all kinds, and to keep an enemy beyond bombarding distance not only from the city but from the camping grounds within it An intrenched camp should consist of a chain of independent forts, with, wherever practicable, a strong inner work; the forts should be as large as possible, and disposed in a right or slightly convex line. No fort should, have undue prominence over the others, as such a fort would be a source of weakness, inasmuch as it might be attacked by itself, and being further removed from the centre< of defensive operations would be more difficult to succour.J The camp should be traversed by free and easy communications; and if it have an interior work, that work should command the whole of the interior. It should also possess facilities for passing rapidly from the defensive to the offensive, and sufficient interior space for the execution of such manoeuvres as are necessary for the defence of the position. I

Fortification of Capitals.

Whether capitals, as capitals, should be fortified has given rise to much difference of opinion; but all authorities are agreed that the capitals of highly centralized countries must be fortified. In such countries the principal resources of the state, both public and private, are collected in the capital; in it is placed the centre of government, and from it administration and organization radiate. Such a capital is truly the heart of the nation; a deadly blow to it stops the national circulation, and national paralysis may and will probably follow. Take, for example, England, perhaps the most highly centralized of countries. Can it be doubted that an enemy in possession of London could exact what terms he pleased ì Upon this point the commissioners appointed to consider the defences of the United Kingdom say,—“There can be no doubt that the main object of an enemy invading the country would be to push for the capital, in the hope that, if he succeeded in obtaining command of it, such a disaster would result in our buying him off upon any terms he might think it expedient to exact.” This was written in i860, but within eleven years its general truthfulness was thoroughly established by the fall of Paris, when the exactions of the Germans were only limited by the ability of the French to comply with them. It is then scarcely too much to say that the fall of London would result in the downfall of England. Speaking of the general confusion and ruin which the presence of a hostile army on British soil must produce, Lord Overstone said: “The occupation of London by an invading army! . . . . I cannot contemplate or trace to its consequences such a supposition.” And he might well say so; not England only, but the cause of civilization throughout the world would be shattered by such an occupation.

At a time when capitals were by no means the national centres which they have since become, owing to the development of the means of locomotion, and to the discoveries of electrical science, Napoleon said that a great capital is the native place of the flower of the nation, the central point of public opinion, and the general depot; and he added that it is the greatest of absurdities to leave so important a place destitute of immediate defence.

How then should a capital be fortified? The answer is, that it should be so fortified that it may be safe from bombardment and from blockade, and that its defences may be beyond the control of its inhabitants.

These objects may be attained by two methods,—first by constructing a circle of detached forts round the capital, and at such a distance in advance of it as shall render investment impossible, or, secondly, by forming a cordon of intrenched camps far in advance of the capital, making at the same time such arrangements as shall facilitate the rapid concentration of troops in any of them.

With respect to these two methods there is much difference of opinion, and eminent military authorities may be cited in support of one or the other according to the bias of the writer. Nevertheless it may be safely asserted that the value of either is dependent upon the number and quality of the troops available for its service. If the troops be few, or insufficiently trained and poor in quality, then it would be proper to have recourse to a system of detached forts round and not far in advance of the capital, and so disposed that they may, in a measure at least, be manned by local auxiliary levies. If, on the other hand, the troops be fully equipped, thoroughly trained and disciplined, with high power of manoeuvring, then, even though inferior in number, it may be advisable to have recourse to a cordon of intrenched camps.

Generally, if circumstances admit of its adoption, the second method is the better, especially if the camps are disposed at such intervals that an enemy in force cannot pass between them, and at such distance from the capital that, if driven out of them, there is still time left to fall back and take up some inner position upon which to deliver a decisive battle. The capital, though well covered by the camps, would take no part in the active defence, and would not be attacked after the fall of one of them, while the occupants of the camps could fight with no apprehension of the populace rising in their rear, a danger to be apprehended from the most patient of people, as they become pinched by the privations and miseries of a siege.

In practice it will almost always happen that a combination of the two methods will be adopted; but whatever method be adopted it will generally be inadvisable to surround the capital, more especially if large, with a close enceinte. If, however, it have such an enceinte, the works of which the enceinte is composed should be provided with strong interior defence. In all large cities there is a considerable cosmopolitan and vagrant element, possessed of no property, and having no interest in the maintenance of order, whose contact with the soldiery may be attended with deplorable results, inasmuch as it must tend to lessen the bands of discipline, to destroy the habits of obedience, and to weaken those feelings of devotion and self-restraint which are more than ever necessary under the privations of a close siege.

Against this view it may be urged that the enceinte constructed round Paris in 1840 prevented its falling into the hands of the Prussians after the battle of Chatillon. This may be true; but in estimating the value of this enceinte it should be borne in mind that 236,000 Prussians were sufficient to shut up in it, and eventually reduce by famine, a garrison of 300,000 men, and it is certain that the absence of interior defences in that enceinte permitted a mere handful of communists to make themselves masters of Paris and its fortifications, and to force back the regular troops upon Versailles. Generally, however, the rapid growth of the population in very large cities precludes a close enceinte. Indeed, the enormous extent of very large capitals, and the very long range of present artillery, render the fortification of them so costly that, in elaborating any scheme for their defence, cost must enter largely into calculation, and must materially modify theoretical and scientific conclusions.

But however elaborately the capital may be fortified, the full effect of the expenditure upon its fortifications is not obtained unless other strong places are formed in appropriate positions in relation to it; for if the capital only be fortified, defence will cease with its fall. It is asserted upon the authority of official documents that the French would not have yielded to the conditions exacted by the conquerors of Paris in 1871, if there had remained to them strong defensive positions such as Orleans, Tours, and Bourges, upon which the armies, poor in quality as they were, of Chanzy, Faidherbe, and Bourbaki could have operated. In fact, if the capital only be fortified, the object of invasion will be limited to it, and the task of the invader will be much simplified, for he will have little fear of his communications, and will be able to make his circle of investment of such strength as seems best to him. And when once the investment is completed, it is matter of great difficulty for the inclosed army, even if superior in numbers, to break out. Its best chance of breaking out is during tho first days of the investment, particularly at the period when the enemy commences to extend himself round the circle of investment, and in so doing presents his flank to it. After the investment is complete, the inclosed army is in a bad position for delivering an attack, as it must advance and deploy under concentric fire playing upon it in front and in flank. The difficulties of such an attack are exemplified in the French attack during the siege of Paris upon the 5th German corps between St Cloud and Buzenval, when 84,000 French attacking from an interior position were defeated with a loss of 6000 men by 20,000 Germans with a loss of only 646.

The advantage of other strong places was shown when 180,000 Germans were detained for a time before Metz. But Metz and Strasburg were so far from Paris that they had scarcely any relation to it. Moreover, they lay close to the frontier; and as here there were no intermediate strong places they were rapidly isolated, and when they fell into the invader’s hands proved of great service to him.

The absence of an intermediate line of defence probably led to the disaster of Sedan and the fatal investment of Paris, while on the other hand the fortresses on the northern frontier, out of date and ill adapted as they were to meet the appliances of modern warfare, enabled Faidherbe’s raw levies to hold their ground as successfully as they did.

If one truth be taught more clearly than another by the Franco-German war, it is the advantage, nay, the absolute necessity, of fortifying, but of properly fortifying, the capital of a highly centralized country. When we consider France deploring the flower of her youth sacrificed, the destruction wrought in her capital, and the spoliation of two of her fairest provinces, and mulcted in a money payment of £200,000,000, with an addition of £170,000,000 more to her debt,—can we avoid the conclusion that no sum spent upon fortifications would have been too large if it had preserved her from such calamities? All that Paris is to France, London is, and more, to the British empire. Paris is rich and populous; London is richer and far more populous. Paris was a tempting prize to an invader; London is more tempting and more accessible. The resources of France in her soil and in her climate are great, and her children are so thrifty that she is self-dependent; but it is far otherwise with Great Britain. She depends upon foreign countries for half the necessaries of life, and the commerce by which her supplies of food are gathered is mainly centred in her capital. France, as we see, has already recovered from the fall of her capital; but the fall of England’s might be without a rise, for it might be attended with a collapse of commerce from which there should be no recovery. Yet notwithstanding the pressure of unheard of ills, and with the regeneration of her army straining her resources heavily, France finds means to spend £4,000,000 upon the fortifications of Paris. With this example before her eyes shall Great Britain in the full tide of prosperity do less for London? (j. e. p. —c. h. n.) [table]