An Emperor Convened the Council That Decided Whether Christ Was God

By the early 320s the Roman Empire's Christians were splitting over a question that today sounds technical and at the time felt existential. A priest in Alexandria named Arius taught that Christ, the Son, was created by the Father — divine, but a created being, with a beginning. His bishop, Alexander, taught the opposite: the Son was eternal and uncreated, the same divine substance as the Father. Both sides had bishops, congregations, and street demonstrations.

Constantine had legalized Christianity in 313. He had no intention of governing an empire fractured by a doctrinal feud he didn't fully understand. In 325 he summoned bishops from across the Christian world to Nicaea (modern İznik, Turkey). Roughly 250 to 318 attended depending on the source. Constantine paid their travel and presided over the opening session himself, despite being an unbaptized catechumen.

The sticking point came down to a Greek word. The proposed creed described the Son as homoousios ("of one substance") with the Father. Arius's allies preferred homoiousios ("of similar substance"). One iota separated the two camps and roughly four centuries of subsequent church politics. The council adopted homoousios. Arius and two stubborn supporters were exiled to Illyricum on June 19, 325; three other bishops signed under imperial pressure and recanted later.

The creed Nicaea produced — refined at Constantinople in 381 — is still recited weekly in Catholic, Orthodox, Anglican, and Lutheran churches. The decision did not, in fact, end the dispute: Arianism kept spreading among Germanic kingdoms for another two centuries. What it established was a precedent: a Roman emperor could call the bishops together, and what they decided would carry imperial as well as theological weight. Church and state had been formally introduced.