Pope Achillas of Alexandria

Pope Achillas of Alexandria, 18th Pope of Alexandria and Patriarch of the See of St. Mark (Archileus), was born in Alexandria, Egypt, and was renowned for his knowledge and piety; this was why Pope Theonas had ordained him priest and appointed him head of the Catechetical School of Alexandria upon the departure of Pierius. He was apparently very highly thought of for his work in Greek philosophy and theological science, as Pope Athanasius the Apostolic later described him by the honorific "Achillas the Great".

As recommended by Pope Peter "Seal of the Martyrs", he was enthroned patriarch in December (Kiahk) 312 AD, after the martyrdom of his predecessor during the reign of Constantine the Great. As soon as he sat on the throne of Saint Mark, Arius beseech him to return him to the participation in the church. With flattery and persuasion, Arius attracted the nobility and the renowned and asked them to intervene for him to the patriarch, so they interceded for Arius to be allowed to participate in the service of the church. Believing that indeed, he was repentant for all his sins, Achillas responded to their request and returned him to his former position, before his heresy, which was priest and preacher. He had thus disobeyed his predecessor, Pope Peter I, because he believed Arius’ pretence of leniency, but the Lord wanted him to remain for only six months, and he departed on the 19th of Paoni (26 June), in 313 AD.

After his departure, Arius nominated himself to become Bishop of Alexandria, but the clergy and the people did not accept his nomination.