Christian priest of Alexandria, Egypt, whose teachings gave rise to a theological doctrine known as Arianism, which, in affirming the created, finite nature of Christ, was denounced by the early church as a major heresy.

An ascetical, moral leader of a Christian community in the area of Alexandria, Arius attracted a large following through a message integrating Neoplatonism, which accented the absolute oneness of the divinity as the highest perfection, with a literal, rationalist approach to the New Testament texts. This point of view was publicized about 323 through the poetic verse of his major work, Thalia (“Banquet”), and was widely spread by popular songs written for labourers and travelers.

The Council of Nicaea (Nicaea, Council of), in May 325, declared Arius a heretic after he refused to sign the formula of faith stating that Christ was of the same divine nature as God. Influential support from colleagues in Asia Minor and from Constantia, the sister of Emperor Constantine I, succeeded in effecting Arius's return from exile and his readmission into the church after consenting to a compromise formula. Shortly before he was to be reconciled, however, Arius collapsed and died while walking through the streets of Constantinople.