Aurelian dedicated the Sol Invictus Temple on Dec 25, 274 in a festival called dies natalis Solis Invicti or birthday of the invincible Sun. It is conjectured to have been promoted by Aurelian as a means of linking this rebirth with the perpetual renewal of the Roman Empire. Also conjectured is that the Natalis Invicti was later renamed Christmas, for example: the Catholic Encyclopedia article on Christmas states: "The well-known solar feast, however, of Natalis Invicti, celebrated on 25 December, has a strong claim on the responsibility for our December date."

Natalis Invicti. The well-known solar feast, however, of Natalis Invicti, celebrated on 25 December, has a strong claim on the responsibility for our December date. For the history of the solar cult, its position in the Roman Empire, and syncretism with Mithraism