Much has been written as to the use of these towers, and the most conflicting theories as to their origin have been propounded. It is, however, fairly certain that they were constructed by Christian builders, both from the fact that they always are or once were near to a church, and also because crosses and other Christian emblems frequently occur among the sculptured decorations of their doors and windows. The original purpose of these towers was probably for places of refuge, for which the solid base and the door high above the ground seem specially adapted. They may also have been watch-towers, and in later times often contained bells. Their circular form was probably for the sake of strength, angles which could be attacked by a battering ram being thus avoided, and also because no quoins or dressed stones were needed, except for the openings—an important point at a time when tools for working stone were scarce and imperfect Both these reasons may also account for the Norman round towers which are so common at the west end of churches in Norfolk, »Suffolk, and Essex, though these have little resemblance to those of Ireland except in the use of a circular plan. One example exactly Eke those of Ireland still exists in the Isle of Man, within the precincts of Peel Castle adjacent to the cathedral of St German; it was probably the work of Irish builders. There are also three in Scotland, viz. at Egilshay in Orkney, and at Abernethy and Brechin.

Round towers wider and low ’ er in proportion than those of Ireland appear to have been built by many prehistoric races at different parts of Europe. Many examples exist in Scotland, and in the islands of Corsica and Sardinia. The towers of this class in Scotland are called “brochs”; they average about 50 feet high and 30 feet in internal diameter. Their walls, which are usually about 15 feet thick at the bottom, are built hoUow, of rubble masonry, with series of passages one over the other running all round the tower. As in the Irish towers, the entrance is placed at some distance from the ground; and the whole structure is designed as a stronghold. The brochs appear to have been the work of a pre-Christian Celtic race. Many objects in bronze and iron and fragments of handmade pottery have been found in and near these towers, all bearing witness of a very early date. See Anderson, Scotland in Pagan Times, 1883, and Scotland in Early Christian Times, 1881. During the 6th century church towers at and near Ravenna were usually built round in plan, and not unhke those of Ireland in their proportions. The finest existing example is that which stands by the church of S. Apollinare in Classe, the old port of the city of Ravenna (see Basilica, vol. iii. p. 415, fig. 5). It is of brick, divided into nine stories, with single-light windows below, three-light windows in the upper stories, and two-lights in the intermediate ones. The most magnificent example of a round tower is the well-known leaning tower of Pisa, begun in the year 1174. It is richly decorated with tiers of open marble arcades, supported on free columns. The circular plan was much used by Moslem races for their minarets. The finest of these is the 13th-century minar of Kootub at Old Delhi, built of Emestone with bands of marble. It is richly fluted on plan, and when complete was at least 250 feet high.

The best account of the Irish round towers is that given by Petrie, in his Ecclesiastical Architecture of Ireland (Dublin, 1845). See also Keane, Towers and Temples of Ancient Ireland (Dublin, 1850); Brash, Ecclesiastical Architecture of Ireland (Dublin, 1875); and Stokes, Early Architecture in Ireland (Dublin, 1878).