Arius, c.256-336, Libyan theologian, founder of the Arian heresy. A parish priest in Alexandria, he advanced the doctrine famous as Arianism and was excommunicated locally (321). He was declared orthodox in Asia Minor, where he had fled (323), but he was anathematized by the Council of Nicaea (see Nicaea, First Council of) and banished by Roman Emperor Constantine (325). But in the reaction after Nicaea, he came into imperial favor. The emperor had ordered the Athanasians at Alexandria to receive him at communion when he suddenly died.

(born circa 250, Libya—died 336, Constantinople, Byzantine Empire) Christian priest and heretic whose teachings gave rise to the doctrine of Arianism. He was leader of a Christian community near Alexandria, Egypt, where he preached doctrines that combined Neoplatonism with a literal, rationalist interpretation of biblical texts. By asserting the absolute oneness and immutability of God, he called into question the divinity of Christ. His views were publicized through his major work, Thalia (circa 323). In 325 the Council of Nicaea declared him a heretic. He was striving to compromise his views and win readmission to the church when he died suddenly in Constantinople. The Arian heresy posed a threat to Christian orthodoxy for several centuries.

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