Eustathius was born in Side, Pamphylia about the year 270. Little is known of his early life. He became [[Bishop]] of Beroea (modern Aleppo), in Syria, about 320. In 325, he was elevated to Bishop of Antioch by the fathers of the [[First Ecumenical Council[[. St. Eustathius was a learned [[
theologians|theologian]] who also had a broad knowledge of secular sciences.
He participated in the First Ecumenical Council in Nicea in 325 and was among the first to preside during the council. He was prominent among the opponents of [[Arius]] and Arianism and zealously fought for the purity of of the Orthodox faith. He continued his battle against the Arians after the council. He refused to welcome any Arian [[priest]]s into his [[diocese]] and conducted a continuous literary attack on them, thus, incurring the hated of the Arians, including [[Eusebius of Caesarea]] and [[Eusebius of Nicomedia]].