Britannica Sources used in this answer

What did the First Council of Nicaea decide about Arianism in 325?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Christology The Transfiguration, the nature of Jesus as the Son of God being revealed to the apostles Peter, James, and John, mosaic icon, early 13th century; in the Louvre, Paris.

At the First Council of Nicaea in 325, the assembled bishops addressed the controversy surrounding Arianism, a doctrine proposed by the Alexandrian presbyter Arius which held that Christ was a created being rather than fully divine.12

The council formally condemned Arianism as a heresy. To safeguard orthodox belief, the council formulated the Nicene Creed, which explicitly affirmed the divinity of Christ by declaring him to be "begotten, not made" and "homoousios" (Greek for "of one substance") with the Father. By invoking this term, the council rejected the Arian view that the Son was of a different essence or had a beginning in time.1234

While the council intended to resolve the dispute, it did not immediately end the conflict; Arianism remained a significant and often dominant theological force in the Eastern Roman Empire for several decades until it was finally proscribed at the First Council of Constantinople in 381.12