- The great river (2,850 kilometers long) that traverses the Balkan Peninsula (q.v.), ending in a large delta before entering the Black Sea (q.v.). Along with the Rhine River (q.v.), at least until the Rhine defenses were abandoned in 406, it comprised the northern border for the Roman Empire (q.v.), and subsequently for Byzantium (q.v.) as well. As a boundary between barbarism and civilization, and a major route of transport, it was guarded by a series of fortresses, yet was hardly an impregnable obstacle for invaders from the north. Nevertheless, the defense of Byzantium's European provinces was closely connected to the defense of the Danubian frontier. After the death of Justinian I (q.v.) in 565, the Danube River was crossed almost at will by Avars and Slavs (qq.v.), who settled south of the river. In 680 the Bulgars (q.v.) settled in the Dobrudja (q.v.), and Byzantium was forced to recognize its independence. The conquest of Bulgaria (q.v.) in 1018 reestablished Byzantine hegemony south of the Danube for a while, but during the 11th and 12th centuries these defenses broke down before the determined assaults of Uzes, Pechenegs, and Cumans (qq.v.).
Historical Dictionary of Byzantium . John H. Rosser .