Sol Invictus

Sol Invictus ("Invincible Sun") was the official sun god of the later Roman Empire. In 274 the Roman emperor Aurelian made it an official cult alongside the traditional Roman cults. Scholars disagree whether the new deity was a refoundation of the ancient Latin cult of Sol, a revival of the cult of Elagabalus or completely new. The god was favored by emperors after Aurelian and appeared on their coins until Constantine. The last inscription referring to Sol Invictus dates to 387 AD and there were enough devotees in the 5th century that Augustine found it necessary to preach against them.

It is commonly claimed that the date of December 25th for Christmas was selected in order to correspond with the Roman festival of Dies Natalis Solis Invicti, or "Birthday of Sol Invictus" but Pope Benedict XVI has argued that the December 25 date was determined simply by calculating nine months after March 25, regarded as the day of Jesus’ conception (the Feast of the Annunciation). This claim was mainly based on a passage of the Commentary on the prophet Daniel by Hippolytus of Rome, which was written around year 204. However, even Pope Benedict has stated that "Christmas acquired its definitive form in the fourth century when it replaced the Roman Feast of the Sol invictus."