Pope Julius I was the bishop of Rome from 6 February 337 to his death on 12 April 352. He is notable for asserting the authority of the pope over the Arian Eastern bishops, as well as setting December 25 as the official birthdate of Jesus.

The date of the birth of Jesus is not stated in the gospels or in any historical sources and the evidence is too incomplete to allow for consistent dating. However, most biblical scholars and ancient historians believe that his birth date is around 4 to 6 BC. Two main approaches have been used to estimate the year of the birth of Jesus: one based on the accounts in the Gospels of his birth with reference to King Herod's reign, and the other by subtracting his stated age of "about 30 years" when he began preaching.