INSTERBURG (16,303), the chief town of a circle in government district of Gumbinnen, East Prussia, is situated at the point where the Angerap and Inster join to form the Pregel, about 55 miles east of Königsberg. It is the seat of an appeal and other courts, and of a reformatory for the district, and has a chamber of commerce, a hospital, a gymnasium, a real-school of the first class, and several other schools. Insterburg is an active manufacturing town, and, besides flax-spinning and iron-founding, carries on the manufacture of machinery, shoes, cement, leather, and furs, along with a considerable trade in cereals, vegetables, flax, linseed, and wood. Close to the town is a large stud-farm, and about 2 miles off is the old castle of Georgenburg. Including the garrison, the population in 1875 was 16,303.

Insterburg was founded in the 14th century as a castle and commandery of the knights of the Teutonic order. The commandery was removed in 1525, but the village which had sprung up round the castle received town privileges in 1583 from the margrave of Brandenburg. During the next century it made rapid advances in prosperity, owing to the settlement in it of several Scotch trading families. In 1679 it was besieged by the Swedes, in 1690 it suffered severely from a fire, and in 1710-11 from a pestilence.