“After the Synod of Jerusalem, Arius went to Egypt, but as he could not obtain permission to hold communion with the Church of Alexandria, he returned to Constantinople. As all those who had embraced his sentiments, and those who were attached to Eusebius, bishop of Nicomedia, had assembled cunningly in that city for the purpose of holding a council, Alexander, who was then ordering the see of Constantinople, used every effort to dissolve the council. But as his endeavors were frustrated, he openly refused all covenant with Arius, affirming that it was neither just nor according to ecclesiastical canons, to make powerless their own vote, and that of those bishops who had been assembled at Nicaea, from nearly every region under the sun. When the partisans of Eusebius perceived that their arguments produced no effect on Alexander, they had recourse to contumely, and threatened that unless he would receive Arius into communion on a stated day, he should be expelled from the church, and that another should be elected in his place who would be willing to hold communion with Arius. They then separated, the partisans of Eusebius, to await the time they had fixed for carrying their menaces into execution, and Alexander to pray that the words of Eusebius might be prevented from being carried into deed. His chief source of fear arose from the fact that the emperor had been persuaded to give way. On the day before the appointed day he prostrated himself before the altar, and continued all the night in prayer to God, that his enemies might be prevented from carrying their schemes into execution against him. Late in the afternoon, Arius, being seized suddenly with pain in the stomach, was compelled to repair to the public place set apart for emergencies of this nature. As some time passed away without his coming out, some persons, who were waiting for him outside, entered, and found him dead and still sitting upon the seat. When his death became known, all people did not view the occurrence under the same aspect. Some believed that he died at that very hour, seized by a sudden disease of the heart, or suffering weakness from his joy over the fact that his matters were falling out according to his mind; other imagined that his mode of death was inflicted on him in judgment, on account of his impiety. Those who held his sentiments were of opinion that his death was brought about by magical arts.”
-Salaminus Hermias Sozomenus in Ecclesiastical History.