The Arian Heresy and the Council of Nicaea

Such were the things Helena accomplished, at a time when the world, under a Christian ruler, had both gained its freedom and found in him an example of faith. But out of that state of peace a far more dreadful danger than all that had gone before fell on all the churches. For then the Arian heresy broke out, and threw the whole world into turmoil with the error it spread. Through the two men named Arius, who were the most active founders of this faithlessness, the emperor himself was led astray; and while he thought he was doing a religious duty, he went on to a violent persecution. The bishops were driven into exile, cruelty was used against the clergy, and even the lay people who had separated themselves from communion with the Arians were punished. [a]

Now the teaching the Arians proclaimed was this: that God the Father had begotten his Son for the purpose of creating the world; that by his power he had made, out of nothing, a new and second God, of a new and second substance; and that there was a time when the Son did not exist. To meet this evil, a synod was called from the whole world to meet at Nicaea. Three hundred and eighteen bishops gathered there. The faith was set out in full in writing, the Arian heresy was condemned, and the emperor confirmed the whole by an imperial decree. After that the Arians did not dare to make any further attempt against the orthodox faith. They mingled with the churches as though they accepted the conclusions that had been reached and held no different opinion. But deep in their hearts there remained a bitter hatred of the catholics; and those they could not defeat in argument about the faith, they attacked with bribed accusers and invented charges.