Why is Christmas celebrated on December 25th? This seemingly simple question may not have the answer you expect.
Secular historians like to explain that the Christians had chosen the birth of Christ to be on December 25th to ‘Christianize’ a pagan feast, the Roman feast of the ‘Birth of the Unconquered Sun.’ However, just the opposite is true: Instituted by Emperor Aurelian in 274 AD, Aurelian implemented the feast to oppose the Christian holy day. Christians had established themselves in the Roman realm along with their political-religious ideology. He wanted to challenge Christmas with his pagan feast.
We know the date of the Nativity from at least the third century. Hippolytus of Rome made mention of it as early as 202 AD. The more authoritative record of the Chronograph of 354 (also known as the Philocalian Calendar), compiled during the reign of Constantine, identifies December 25th as the feast day of the birth of Jesus Christ.
Some attempt at identifying the Christmas date was made by second-century Christians in Rome. They related His birth to the exact day of Jesus’ death. These Latin Christians (as opposed to Greek Christians) understood that Christ’s death had occurred on Friday, March 25th, of the year 29 AD. As it turns out, this date would have been impossible to be the true date of the death of Christ, since March 25th was not a Friday, but that is another question.
Another attempt at pinpointing the Christmas date was through assumptions about the life cycle of prophets. There was a widespread belief within first-century Judaism in the ‘perfect age’ of the Jewish prophets; the prophets of Israel were believed to have died on the same day they were born or conceived, to have lived to a ‘perfect’ age—a perfect life, in temporal understanding.
This idea was applied to Jesus from earliest Christianity onwards. Since Jesus had died on March 25th, it could be assumed that—by having lived to a ‘perfect age’—he had also been conceived on March 25th. The liturgy celebrates the Feast of the Annunciation of the Lord on March 25th to this day. As could be assumed—considering that a child is carried in the womb for nine months—the birth came about nine months after March 25th, that is, on December 25th.
So the birth of Jesus Christ has nothing to do with the adoption of a pagan festival, but was from the beginning a practice of the early Church, due to older, traditional beliefs. December 25th remains an uncertain date of Christ’s birth, but rather than coming to be as the Christianizing of a pagan festivity, it is the result of well-thought-out, traditional Christian symbolism and calculation.