Because of his heretical teachings, Arius was condemned and deprived of his office. He fled to Palestine and spread his doctrine among the masses through popular sermons and songs, and among the powerful through the efforts of influential leaders, such as Eusebius of Nicomedia and, to a lesser extent, Eusebius of Caesarea. The civil as well as the religious peace of the East was threatened, and Roman Emperor Constantine I convoked (325) the first ecumenical council (see Nicaea, First Council of). The council condemned Arianism, but the Greek term homoousios [consubstantial, of the same substance] used by the council to define the Son's relationship to the Father was not universally popular: it had been used before by the heretic Sabellius. Some, like Marcellus of Ancyra, in attacking Arianism, lapsed into Sabellianism (see under Sabellius).
Eusebius of Nicomedia used this fear of Sabellianism to persuade Constantine to return Arius to his duties in Alexandria. Athanasius, chief defender of the Nicene formula, was bishop in Alexandria, and conflict was inevitable. The Eusebians managed to secure Athanasius' exile, and when the Arian Constantius II became emperor, Catholic bishops in the East, e.g., Eustathius, were banished wholesale.
Athanasius' exile in Rome brought Pope Julius I into the struggle. A council wholly favorable to Athanasius, convened at Sardica (c.343), was avoided by the Eastern bishops and ignored by Constantius. The Catholics were left dependent on Rome for support. After the West fell to Constantius, the Eusebians reversed the decisions of Sardica in several councils (Arles, 353; Milan, 355; Boziers, 356), and Pope Liberius, St. Hilary of Poitiers, and Hosius of Cordoba were exiled. The victorious Arians, however, had now begun to quarrel among themselves.