He was a disciple of Athanasius of Alexandria who designated him as his successor before his death in 373.
[2][3] The Arians opposed his appointment and shortly after his consecration, the prefect Palladius, acting on orders from Emperor Valens drove him from the city and installed Lucius, an adherent of Arianism as bishop.
[4][5] Pope Damasus I, hearing of this new persecution, sent a deacon with a letter of communion and consolation for Peter; the messenger was arrested, treated as a criminal, savagely beaten, and sent to the mines of Phenne.
[2] Peter remained for some time in concealment, and then found refuge at Rome, where Damasus received him and gave him support against the Arians.
Peter returned to Alexandria in the spring of 378,[2] where Lucius yielded out of fear of the populace.