The Roman emperor Theodosius (ca. 346-395) was sometimes called "the Great" because of his solution of the Gothic problem and unification of the empire and because of his championship of orthodoxy, which earned for him the extravagant praise of Catholic writers.
Theodosius was the son of a famous general of the same name who had cleared Britain of northern invaders and then had quashed a Moorish rebellion. However, the general was falsely accused at court and summarily executed in 376. Theodosius had served ably under his father in Britain, and later, in an independent command in Moesia, he had saved the province from barbarian invasion. At his father's death, however, he gained permission to retire to his family estate in Spain.
In August 378 the Eastern Roman emperor, Valens, was overwhelmed and killed at Adrianople by invading Goths. The Western emperor, Gratian, thereupon recalled Theodosius from retirement and in January 379 made him joint emperor with command over the East. Instead of fighting the Goths directly with demoralized Roman troops, by diplomacy Theodosius fostered dissensions among them, won the friendship of the Visigoths by his courteous treatment of their king, and ultimately allowed the Visigoths to remain within the empire, though they retained their own political cohesion under native chieftains. They were called allies (foederati) rather than subjects; and this set the legal precedent for the ultimate partition of much of the empire among immigrant barbarians.
In 383 Magnus Maximus was proclaimed emperor by British troops, and Emperor Gratian was murdered. Theodosius at first accepted his new colleague and allowed him Britain and Gaul; but when, in 387, Maximus drove from Italy Gratian's young half brother Valentinian II, Theodosius (now the husband of Galla, Valentinian's sister) marched west, destroyed Maximus, and restored Valentinian. Theodosius remained in Italy for 3 years, leaving the administration of the East to his elder son, Arcadius, whom he had declared an augustus (coruler) in 383.
In 391 Valentinian was murdered by his Frankish military commander, Arbogast, who then raised one Eugenius to the throne. Theodosius again returned to the West and defeated the usurper in the autumn of 394. The empire was then briefly reunited under one ruler; but Theodosius himself died on Jan. 17, 395, leaving the East to Arcadius and the West to a younger son, Honorius, who had been proclaimed augustus in 393. This division of the empire became permanent.
A serious illness soon after his accession prompted Theodosius's early baptism, which Christian Roman emperors usually postponed till their deathbeds. This made him very susceptible to the pressures of the Church, and he came particularly under the influence of Ambrose, the strong-willed bishop of Milan, who repeatedly placed him under heavy penance when his justice was hotheaded or severe. Theodosius was a devoted persecutor of Christian heresies, and in 391 he officially closed all the empire's temples and forbade the practice of all pagan cults.
Noel Q. King, The Emperor Theodosius and the Establishing of Christianity (1960), discusses the important role of Theodosius in the triumph of orthodox Catholicism; and A. H. M. Jones, The Later Roman Empire (1964), covers the secular aspects of his reign.
Williams, Stephen, Theodosius: the empire at bay, London: Batsford, 1994.