The exact date of Jesus’ birth is unknown. The Bible does not give specifics on the date of either Jesus' birth or conception. In the second century A.D., a Roman Christian historian named Sextus Julius Africanus calculated Jesus’ birthdate to be December 25 (nine months after Africanus believed Jesus was conceived). In spite of the assumptions made in Africanus’s line of thinking, the date was widely accepted.

At that time, Roman culture already celebrated a holiday on December 25: Saturnalia, the winter solstice. This tradition honored Saturn, the god of agriculture, and was celebrated with merriment, feasting, and gift giving. When Rome eventually instituted Christianity as the state religion in the fourth century, the Roman church converted the week-long Saturnalia to a Christian holiday in order to commemorate Jesus’ birth. Christians have celebrated it as such ever since.