THEODOSIUS I, ROMAN EMPEROR. - Born at Cauca on 11 January 347, died at Milan on 17 January 395. Having entered the army, he followed his father in the campaigns in Britain and Africa, but after his father's tragic death (376) he retired to private life. He was recalled to service by Gratian after the battle of Adrianople (378) with the rank of magister equitum; shortly afterwards he was named Augustus (January 379) and the Eastern Empire was entrusted to him. He immediately set to work with prudent military and diplomatic action to pacify those provinces, crushing the ambitions of the barbarians who were plundering the frontiers.
In August 383 Magnus Maximus was proclaimed emperor by the soldiers of Britain, and descended into Gaul; Gratian, abandoned by his troops, took refuge at Lyon, but was betrayed and killed by the governor of the city. T., compelled by pressing events, accepted the accomplished fact and recognized Maximus's government of Britain, Gaul and Spain. In 387, however, the usurper descended into Italy with the evident aim of seizing it; Valentinian II together with his mother Justina fled to Thessalonica. T. could tolerate this no longer and, having pacified the eastern frontiers of the Empire by an agreement with Persia, marched against Maximus; the latter was defeated at Poetovio and, having taken refuge at Aquileia, was betrayed by his own soldiers and killed (August 388). While the general Arbogast pacified Gaul by defeating Maximus's son, Flavius Victor, T. remained in Italy until 391. During this period he had his two famous conflicts with St. Ambrose, in which the Saint succeeded, in the name of his spiritual authority, in imposing his will on the fiery Emperor. At Callinicum (Cappadocia) the Christians had burned the synagogue; T. ordered that it be rebuilt at the expense of the bishop of the city, but Ambrose obtained the revocation of the order (St. Ambrose, Epist., 40 ff.: PL 16, 1148-69). More important and more notorious was the affair of Thessalonica; there the citizens, who had been unable to obtain the release of a charioteer, had risen up and killed the authorities. T. ordered a reprisal in which several thousand people were massacred. St. Ambrose protested energetically against the brutal act and wrote a letter to the Emperor threatening him with excommunication if he did not do penance; after tergiversations T. humbly submitted to the bishop's injunctions and at Christmas of 390 was readmitted to Communion (St. Ambrose, Epist., 51: De obitu Theodosii: PL 16, 1209-14, 1447-68).
Having returned to the East, T. still had to fight against the barbarians, with whom, after defeating them, he concluded a peace treaty in 392. In the West, however, another usurper arose; the general Arbogast, after the death of Valentinian II (May 392), perhaps having had him assassinated, had the rhetorician Flavius Eugenius proclaimed emperor. Leaning on the pagan party, led by the praetorian prefect Nicomachus Flavianus, Eugenius came into Italy; T. marched against him and defeated him near the river Frigidus (Friuli): Eugenius and Arbogast were killed in the fighting (summer 394). The Roman Empire once again returned to the hands of a single sovereign worthy and capable of ensuring well-being and tranquillity for all, but the hopes were soon frustrated, since, having fallen gravely ill, T. died at Milan in January 395, leaving as heirs his two sons Arcadius and Honorius, whom he had already named Augusti in 393.
If T.'s activity was beneficial to the Empire, his religious policy with regard to Catholicism and paganism was no less important; he indeed sanctioned the definitive triumph of the former over the various heretical sects and accelerated the disappearance of the latter, which still had fanatical supporters in the senatorial class. T. did not act directly against persons, but by continuing the policy of Constantius II and Gratian he succeeded in fully attaining his goal. In 381 and 383 he deprived apostates of their civil rights (Cod. Theod., XVI, 7, 1-2). After the death of Gratian he sent the prefect Cynegius to Egypt with the explicit order to forbid idolatry and close the temples. Finding himself in Rome, after the victory over Maximus, he rejected the repeated requests of the Senate asking for the restoration of the altar of Victory, and indeed in a speech he exhorted the senators themselves to abandon their pagan superstitions and embrace Catholicism. Shortly afterwards he removed all state contributions for the cult of the temples and forbade every public pagan ceremony for Rome, threatening grave penalties against the authorities who tolerated them (ibid., XVI, 10, 10); the same decree was extended to Egypt (ibid., XVI, 10, 11) and in 392 to the whole Empire, establishing fines and confiscations against transgressors (ibid., XVI, 10, 12). Finally, after the victory over the usurper Eugenius, he applied with greater rigor all the laws previously issued against paganism.
This action carried out by T. against idolatry, besides being inspired by his sentiment as a convinced Christian, also sprang from the recognition that paganism could no longer sustain the old Empire, threatened on every side by the barbarians; only Christianity could infuse it with new lifeblood and, permeating it with its catholicity, could save it and preserve its perpetuity. The true and only Christianity of T. could therefore be none other than the Catholic one, the same that Peter had preached at Rome and that his successor Damasus taught (ibid., XVI, 1, 2). From this derives his entire religious policy in combating heresies and in particular the one which in the 4th century more than any other had attacked Catholic orthodoxy: Arianism. Already from the beginning of his reign, having fallen ill at Thessalonica, he asked for Baptism from the local bishop, but before receiving it he wished to make sure that he was orthodox. Having settled at Constantinople in 380, his first care was to induce the Arian patriarch Demophilus to adhere to the Catholic faith, and since the latter refused he recognized the Catholic St. Gregory, to whom he restored all the churches of the city (ibid., XVI, 5, 6). He took part in the Council of 381 and confirmed its decisions against the heretics (ibid., XVI, 1, 3). In 383 he wished to attempt a pacification among the various sects, and summoned their leaders to Constantinople to examine their respective professions of faith; the discussions led to nothing, and so T., having accepted the Catholic one, had all the others burned, and promulgated several edicts forbidding any assembly of heretics (ibid., XVI, 5, 11-13).
T.'s manifold legislative activity thus soon led to the total disappearance of Arianism in the Empire.