EUSEBIUS (OF NICOMEDIA) (d. 341?), Greek bishop and theologian, was the defender of Arius more avowedly than his namesake of Caesarea, and from him the Eusebian or middle party specially derived its name, giving him in return the epithet of Great. His first bishopric was Berytus (Beirut) in Phoenicia, but his name is especially identified with the see of Nicomedia. He wrote a letter in defence of Arius to Paulinus, bishop of Tyre, which is preserved in the Church History of Theodoret. He ap pears to have been agreed with Eusebius of Caesarea in placing Christ above all created beings, the only begotten of the Father, but in refusing to recognize him to be "of the same substance" with the Father, who is alone in essence and absolute being.
At the council of Nicaea Eusebius of Nicomedia earnestly op posed the insertion of the Homousian clause and refused to sign the anathema directed against the Arians, "because he doubted whether Arius really held what the anathema imputed to him" (Sozom. ii. 15). After the council his zeal against the Athanasians led to his temporary banishment from his see but through the in fluence of the emperor's sister Constantia he was promoted to the see of Nicomedia, and by her favour he was later restored to his position. He was promoted in 339 to the see of Constantinople and became the leader of the anti-Nicene party till his death (c. 341). (See ARIUS.)