Christmas is the annual celebration practiced by Christians that commemorates the birth of Christ. The word is a contraction of “Christ’s mass.” The practice did not come into being until “A.D. 336, the date apparently chosen to counter the Roman feast Natalis Solis Invicti (“birth of the unconquered sun”), the birthday of Emperor Aurelius.[note]Myers, Allen C. The Eerdmans Bible Dictionary. Grand Rapids, MI: Eerdmans, 1987.[/note] This feast fell upon December 25, which coincided with the winter solstice. As Christianity spread, it replaced many of the pagan festivals with Christian ones, and December 25 became known as the birth of Christ. Of course, no one knows in which month Christ was actually born.