THEODOSIUS (c. 347–395), Roman emperor (379–395). In the worst disaster since the days of Hannibal the Roman army and the emperor Valens were wiped out near Hadrianopolis by the Goths in August 378. The senior surviving emperor, the young Gratian, summoned from his Spanish homeland a certain Theodosius who was elevated as emperor in January 379 at the age of 33. His first task was to come to terms with the barbarian invaders. He allowed them to settle and used them as federated troops. He dealt with the other military threat, Persia, by establishing a policy of coexistence that yielded a century of peace.

Since religious stability was accepted as the architectonic element through which the empire was held together, it occupied Theodosius's continuous attention. It is not easy to tell exactly how much of subsequent imperial policy was initiated by the emperor himself. It may be supposed that his influence on the...