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How did the First Council of Nicaea respond to Arianism?

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St. Ambrose Image of St. Ambrose, detail from a stained-glass window in a Roman Catholic church in Antwerp, Belgium.

The First Council of Nicaea, convened in 325 CE, responded to Arianism by formally condemning the doctrine as a heresy.12

To safeguard orthodox Christian belief, the council issued a creed that explicitly affirmed the divinity of Christ. Central to this statement was the use of the term homoousios (Greek for "of one substance"), which declared that the Son is completely divine and of the same substance as the Father, directly contradicting the Arian view that Christ was a created being.123

Despite this condemnation, the council did not immediately resolve the controversy. Arianism remained a significant and often influential force within the Roman Empire for decades, continuing to spark theological and political disputes until it was finally proscribed at the First Council of Constantinople in 381 CE.12