Saint Achillas was a bishop and a theologian during an era of dispute in the church. He was the bishop of Alexandria in Egypt, which was one of the most powerful cities at that time.
A bishop named Arius was ordained later on. Saint Achillas recognized the untruths in Arius preaching. He defended the faith but Arius attacked him. A council was put together to condemn Arius for his false preachings. He was forced to flee to Palestine.