Pope Julius I

Julius became bishop of Rome on 6 February 337, stepping into an empire where Arian bishops held sway in the East. When Athanasius, patriarch of Alexandria, was deposed by those bishops, he appealed to Julius. Julius condemned the deposition as unjust and threw his support behind Athanasius, setting himself against the Arian faction. The move became a test case: Julius asserted that Rome's authority extended over the Eastern bishops, a claim they did not welcome. He also receives credit for fixing December 25 as the official birthdate of Jesus, a date that stuck. He died on 12 April 352, fifteen years into a papacy defined by boundary-setting.