EUDOXIUS. - One of the principal leaders of Arianism in the 4th century, bishop of Constantinople from 360 to 370. Born at Arabissos, in Lesser Armenia, he attended in Antioch the lectures of the holy martyr Lucian (d. 311), and afterward went over to Arianism. As bishop of Germanica, he took part in the Antiochene Synod of 341, called the Synod of the Dedication. He was moreover present at most of the numerous synods convened by Constantius: at Sardica in 343, among the Easterners; probably at Sirmium in 351; certainly at Milan in 355 and at Sirmium in 357. From that city, on the announcement of the death of Leontius, the Arian bishop of Antioch, he set out in haste to obtain the succession to that see. He succeeded by trampling on the canons, in spite of the protests of the electing bishops. From this moment he declared himself openly in favor of rigid Arianism, or Anomoeanism, represented by Aetius and Eunomius. But he soon found himself in difficulties, since the emperor Constantius had come out in favor of the semi-Arianism and homoiousianism of Basil of Ancyra, after the Council of Ancyra of 358. Having run the risk of being exiled and deposed, he temporarily withdrew from Antioch. But he soon had his revenge alongside Acacius of Caesarea, with whom he contributed to the triumph of the formula of Rimini-Constantinople, that is, of Homoeanism, which became the official Arianism. Constantius rewarded him for such dogmatic complaisance by transferring him to the see of Constantinople (360), which he occupied until his death (370). If he managed to keep that position, he owed it to the protection of the Arian emperor Valens, whom he himself baptized before the expedition against the Goths (366-67).
E. was an ambitious man without character and without firm convictions. The Arian Philostorgius describes him as a lovable man, of irreproachable conduct, but timid to the point of cowardice. Of his writings, which, it seems, were numerous, there remain only fragments of doubtful authenticity and a brief profession of faith, derived from a treatise on the Incarnation: Λόγος περί αἰφιώσεως (cf. P. Caspari, Alte und neue Quellen zur Geschichte des Taufsymbols und der Glaubensregel, Christiania 1879, pp. 170-85)