The meeting that defined what Christianity believes about Jesus

The Arian controversy began in Alexandria around 318 AD when a priest named Arius began teaching that the Son of God was not co-eternal with the Father but had been created, the first and greatest of all creatures, but a creature nonetheless. The formula attributed to him was "there was a time when he was not." The position spread rapidly because it was, in some ways, easier to comprehend than its alternative.

Emperor Constantine, recently victorious and eager for unity across an empire he had just consolidated, called a council at Nicaea in 325 AD to settle the matter. Approximately 300 bishops attended. The debate was not a polite theological seminar. It involved personal confrontations, accusations, and at least one account of Arius being struck by Nicholas of Myra, the historical Santa Claus, though this story is disputed.

Athanasius, the bishop's deacon at the time, was not a bishop and could not vote. He argued on the floor with a passion that made him enemies. His position, that the Son was of the same substance as the Father, homoousios, was adopted in the council's creed. Arius was condemned and exiled.

The controversy did not end there. Over the following decades, various emperors favoured different positions, and Athanasius was exiled five times, sometimes by emperors, sometimes by councils that reversed Nicaea's decision. He spent a total of 17 years in exile. He is remembered by the phrase "Athanasius contra mundum, meaning Athanasius against the world.

The Nicene Creed, finalised at the Council of Constantinople in 381 AD, is the form still recited in Catholic, Orthodox, Anglican, and many Protestant liturgies today. The line "God from God, Light from Light, true God from true God, begotten not made, of one substance with the Father" is the direct result of Athanasius's refusal to yield when the consensus was against him.