THEODOSIUS I, " the Great," son of Theodosius, Valentinian's great general, who in 368-69 drove back the Picts and Scots from the Roman territories in Britain and suppressed the revolt of Firmus in Mauretania (372). Shortly after (376), the elder Theodosius was put to death by order of Valens, probably through fear lest he should be the Theodosius or Theodore whom a magician had indicated as the future emperor. The younger Theodosius was born about the year 346. He was a native of Spain, but the exact place of his birth is uncertain (Cauca in Galicia according to Idatius and Zosimus, Italica according to Marcellinus). He accompanied his father into Britain (368), and a little later distinguished himself by defeating the Sarmatians who had invaded Moesia (374). On his father's death he retired to his native place, where he lived quietly till after the great battle of Adrianople (August 9, 378), when Gratian summoned him to share the empire. After gaining some fresh victories over the Sarmatians, Theodosius was made Augustus at Sirmium on the 19th of January 379, and was assigned all the eastern provinces, including part of Illyricum. It was a time of great peril for the Roman state. While the Visigoths were carrying their raids up to the walls of Constantinople, bands of Ostrogoths, Taifali, Huns and Alans joined them in overrunning the Balkan countries. In 379 Theodosius, after reorganizing the army at Thessalonica, carried on a successful campaign of skirmishes along the Danube and induced numerous Gothic bands to give in their allegiance; his lieutenant Modares, a Gothic refugee, defeated the invaders severely in Thrace. At the end of the year Theodosius went to Constantinople to be crowned. Returning to Thessalonica in 380 he was kept out of the field for some time by a serious illness. In this year or the next he was called upon to meet two armies of invaders. He conducted in person the war against the Visigoths under Fritigern (in Macedonia and Epirus), and on one occasion was nearly betrayed into the enemy's hands; this campaign, in which Gratian's general Arbogast eventually lent help, was ended by Fritigern's death. The defence of the Danube against the Ostrogoths under Alatheus and Safrax was entrusted to the general Promotus, who severely defeated the enemy in an attempt to cross the river. Theodosius attained even greater successes by his diplomacy. He persuaded the fugitive Visigoth king Athanaric to enter his service, and enlisted 40,000 of his former enemies as foederati, providing them with settlements in various parts of the realm. Though this kindness towards the Germanic tribes was resented by the Romans, and in some cases ill requited, yet it may be said that it not only averted a great danger to the empire, but considerably strengthened Theodosius' army. In 382 the pacification of the Balkans was complete. In 386 Promotus checked a new attempt at invasion on the Danube.
In 383 Theodosius created his eldest son Arcadius Augustus. The same year saw the revolt of Maximus in Britain and the murder of Gratian. For five years Theodosius consented to accept the usurper as his colleague; but when Maximus attempted a few years later to make himself master of Italy Theodosius advanced against the invader and overthrew him near Aquileia (July 28, 388). This victory was followed by the murder of Maximus and his son Victor, after whose death Theodosius conferred upon Valentinian II. all that part of the empire which his father had held. After celebrating a triumph in Rome (389) he stayed to arrange the government of Italy for another two years. If we may trust the evidence of Zosimus, from the end of the year 388 Theodosius resigned himself to gluttony and voluptuous living, from which he was only roused by the news that in the Western empire Arbogast had slain the young Emperor Valentinian and set up the grammarian Eugenius in his stead (May 15, 392).
Theodosius made extensive levies and with a force partly composed of barbarian auxiliaries marched out against Eugenius. The armies met near the river Frigidus, some thirty-six miles distant from Aquileia. On the first day Theodosius' barbarians, engaging with those of the hostile army, were almost destroyed, and the victory seemed to be with Eugenius. After a night of prayer, towards cockcrow the emperor was cheered by a vision of St Philip and St John, who, mounted on white steeds, promised him success. On the second day the issue was doubtful till, if we may trust the concurrent testimony of all the contemporary church historians, a sudden gust of wind blew back the enemy's arrows on themselves. This was the turning-point of the battle: Eugenius was slain by the soldiers; and two days later Arbogast com-, mitted suicide (September 5-9, 394). From the north-eastern parts of Italy Theodosius passed to Rome, where he had his son Honorius proclaimed emperor under the guardianship of Stilicho. Thence he retired to Milan, where he died of dropsy (January 17, 395), leaving the empire to be divided between his two sons Honorius and Arcadius.
Important as the reign of Theodosius was from the political point of view, it is perhaps still more so from the theological. According to Sozomen, his parents were both orthodox Christians, according to the creed sanctioned by the council of Nicaea. It was not, however, till his illness at Thessalonica that the emperor received baptism at the hands of Bishop Ascholius, whereupon, says the same historian, he issued a decree (February 380) in favour of the faith of St Peter and Pope Damasus of Rome. This was to be the true Catholic faith; the adherents of other creeds were to be reckoned as heretics and punished. The great council ot Constantinople, consisting of 150 orthodox and 36 Macedonian bishops, met in the following year, confirmed the Nicene faith, ordered the affairs of the various sees, and declared the bishop of Constantinople to rank next to the bishop of Rome. The emperor cannot be acquitted of the intolerance which marks edicts such as that depriving apostatizing Christians of the right of bequest. It was not till 389 or 390 that he issued orders for the destruction of the great image of Serapis at Alexandria. Other edicts of an earlier or later date forbade the unorthodox to hold assemblies in the towns, enjoined the surrender of all churches to the catholic bishops, and overthrew the heathen temples " throughout the whole world." During the reign of Theodosius Gregory of Nazianzus was made bishop of Constantinople. In 383 Theodosius called a new council for the discussion ot the true faith. The orthodox, the Arians, the Eunomians and the Macedonians alt sent champions to maintain their special tenets before the emperor, who finally decided in favour of the orthodox party. He seems to have suffered the Novations to hold assemblies in the city. Perhaps the most remarkable incident in the life of Theodosius from a personal point of view is the incident of his submission to the reprimands of Ambrose, who dared to rebuke him and refuse to admit him to the Eucharist till he had done public penance for punishing a riot in Thessalonica by a wholesale massacre of the populace. Equally praiseworthy is the generous pardon that the emperor, after much intercession, granted to the seditious people of Antioch, who, out of anger at the growing imposts, had beaten down the imperial statues of their city (387). When the Christians in the eastern part of the empire destroyed a Jewish synagogue and a church belonging to the Valentinians, Theodosius gave orders for the offenders to make reparation. Such impartial conduct drew forth a remonstrance from Ambrose, who, where the interests of his creed were concerned, could forget the common principles of justice.
Theodosius was twice married (i) to Aelia Flacilla, the mother of Arcadius (377-408) and Honorius (384-423) ; (2) to Galla (d. 394), the daughter of Valentinian I.
The chief authorities for the age of Theodosius are Ammianus Marcellinus, Zosimus, Eunapius and the ecclesiastical historians (Socrates, Sozomen, Theodoret). Much information may also be gleaned from the writings of St Ambrose, St Gregory of Nazianzus, Isidore of Seville, and the orators Pacatus, Libanius, Themistius. Among modern authorities see: E. Gibbon, The Decline and Fall of the Roman Empire (ed. Bury, London, 1896), chaps. 25 and 27; T. Hodgkin, Italy and her Invaders (Oxford, 1892), chaps. 5, 6, 8-1 1 ; A. Giildenpenning and J. I Hand, Der Kaiser Theodosius der Grosse (Halle, 1878); G. R. Sievers, Studien zur Geschichte der romischen Kaiser (Berlin, 1870), pp. 283-333.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)