THEODOSIUS I., THE GREAT, son of Theodosius the Elder; one of the most notable and most capable of the later Ro man emperors; born in Cauca, Spain, about 346; served under his father in Britain, Germany, and Africa, and won fame as a general by his exploits in Mcesia. On his father's death he retired to his native farm, whence he was sum moned by Gratian to become his col league in the purple and emperor in the East (379). It was a critical time. The Goths, too numerous and formidable to be attacked en masse, flushed, too, with their recent Cannm like victory at Ad rianople and the total defeat of his pre decessor Valens, were roaming the coun try at will. His military reputation was equal to the strain. He made Thessa lonica his headquarters, and within four years broke up the vast Gothic army, attached many of its members to the empire as faithful soldiers and allies, and restored tranquillity to the troubled coun try S. of the Danube.
A serious illness in 380 led to his bap tism as a Trinitarian, and, as a conse quence, to the restoration of the religious unity of the empire and the promulgation of various edicts against Arianism and other heresies. He appointed Gregory Nazianzen Archbishop of Constantinople, and summoned the second general coun cil, which met there (381) to supplement the labors of Niciea. The murder of Gra tian at Lyons, the advance toward Italy of the upstart Maximus proclaimed em peror in Britain, and the arrival of Va lentinian II. (with his mother Justina and his sister Galla) begging for help led to Theodosius' marriage with Galla, to his victory at Aquileia (388), and to the restoration of his youthful colleague. Hereafter for some years Theodosius lived at Milan enjoying the friendship and respect of its bishop St. Ambrose.
Theodosius was able, just, even gener ous, virtuous, and religious, but inclined to indolence and of a passionate temper. He had canceled, on the entreaties of its bishop and the penitence and humiliation of its leading citizens, the severe meas ures meted out to Antioch after a riot (387) in which the imperial statues had been contemptuously overthrown; but in 390, when the governor of Thessalonica was lynched by a circus mob for his pun ishment of a brutal but favorite chariot eer, Theodosius, in spite of expostula tions, ordered the people of the city to be invited into the circus and there massa cred. At least 7,000 were thus put to death. Thereupon Ambrose wrote to Theodosius upbraiding him for the deed, and later withstood his attempt to enter the church at Milan. The bishop only readmitted the emperor to the sacrament after eight months' retirement and pub lic penance performed in the face of the whole congregation. In 392 Valentinian II. was murdered and in 394 Theodosius, then at Constantinople, again marched W., this time against the Frankish gen eral Arbogast and his puppet, Emperor Eugenius. After a stubborn fight at the Frigidus river, lasting two days, Theodo sius gained a complete victory, and for four months ruled as sole Roman em peror. He expired in the arms of Am brose on Jan. 17, 395. Almost imme lately thereafter followed the barbarian invasions of Greece and Italy, which led directly to the subsequent Teutonic set tlements in the S. and indirectly to the formation of the kingdoms of modern Europe.