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Why did Constantine call the Council of Nicaea in 325?

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Mosaic: Christianity — Christianity Christ as Ruler, with the Apostles and Evangelists (represented by the beasts). The female figures are believed to be either Santa Pudenziana and Santa Práxedes or symbols of the Jewish and Gentile churches. Mosaic in the apse of Santa Pudenziana basilica, Rome, 401–417 ce.

Emperor Constantine convened the First Council of Nicaea in 325 primarily to resolve the Arian controversy, a significant theological dispute that threatened the unity of the Christian church.123

The conflict centered on the teachings of Arius, who argued that Christ was a created being rather than divine and equal to God the Father. This debate caused deep divisions within the church, which Constantine viewed as a threat to the stability of the Roman Empire. By calling the council, Constantine sought to establish a unified definition of the faith, ultimately leading the assembly to condemn Arianism as heresy and affirm the divinity of Christ through the term homoousios (of one substance).132

This event marked a precedent for imperial involvement in ecclesiastical affairs, reflecting the growing alliance between the church and the state during Constantine's reign.23