The central issue of the Council at Nicea was [[Arius]] and his teaching [[Arianism]]. Alexander supported [[Alexander of Alexandria]] in the defense of the Trinitarian position at the council that in the end resulted in the council’s condemnation of Arius and Arianism. After the council, Arius wanted to be received back into communion. With the support of [[Eusebius of Nicomedia]], who convinced him, [[Constantine the Great|Constantine I]] commanded Alexander to formally receive Arius back into communion. <ref>[[Athanasius of Alexandria]] ''Ep. ad Serap.''; Rufinus, ''Hist.'' i.</ref> According to Socrates Scholasticus, Arius did not in fact repent of his heresy, but was equivocating, of which Bishop Alexander was aware.<ref>Socrates Scholasticus, ''op. cit.'' i. 37</ref> Alexander, though threatened by the Eusebians with [[deposition]] and banishment, persisted in his refusal to admit Arius back into the Church. Alexander shut himself up in the Church of Hagia Irene, which at that time was the [[cathedral]] of Constantinople, in fervent prayer that God would take him from this world rather than be forced to restore someone to communion who he feared was only feigning [[repentance]]. As it happened, Arius died in 336 on his way to the church, before he could be received back into communion.
Alexander did not long survive Arius.<ref>Socrates Scholasticus, ''op. cit.'' ii. 6 ; Theodoret, ''op. cit.''i. 19</ref> On his deathbed he was said to have nominated his vicar, [[Paul I of Constantinople|Paul]] as his successor, and to have warned his [[clergy]] against [[Macedonius]], a [[Semi-Arianism|semi-Arian]] who became bishop of Constantinople in 342 and whose teachings inspired [[Macedonianism]].