In about 319, when Athanasius was a deacon, a presbyter named Arius came into a direct conflict with Alexander of Alexandria. It appears that Arius reproached Alexander for what he felt were misguided or heretical teachings being taught by the bishop. Arius's theological views appear to have been firmly rooted in Alexandrian Christianity, and his Christological views were certainly not radical at all. He embraced a subordinationist Christology which taught that Christ was the divine Son (Logos) of God, made, not begotten, heavily influenced by Alexandrian thinkers like Origen, and which was a common Christological view in Alexandria at the time. Support for Arius from powerful bishops like Eusebius of Caesarea and Eusebius of Nicomedia, further illustrate how Arius's subordinationist Christology was shared by other Christians in the Empire. Arius was subsequently excommunicated by Alexander, and he would begin to elicit the support of many bishops who agreed with his position.

What made Arius's belief about Jesus different from Alexander's?