Many Christians think that Christians celebrate Christ’s birth on December 25th because the church fathers appropriated the date of a pagan festival. Almost no one minds, except for a few groups on the fringes of American Evangelicalism, who seem to think that this makes Christmas itself a pagan festival. But it is perhaps interesting to know that the choice of December 25th is the result of attempts among the earliest Christians to figure out the date of Jesus’ birth based on calendrical calculations that had nothing to do with pagan festivals.The date of birth was connected to the date of death in this reasoning.
Rather, the pagan festival of the “Birth of the Unconquered Son” instituted by the Roman Emperor Aurelian on 25 December 274, was almost certainly an attempt to create a pagan alternative to a date that was already of some significance to Roman Christians. Thus the “pagan origins of Christmas” is a myth without historical substance.
Greek Christians seem to have wanted to find a date equivalent to 14 Nisan in their own solar calendar, and since Nisan was the month in which the spring equinox occurred, they chose the 14th day of Artemision, the month in which the spring equinox invariably fell in their own calendar. Around A.D. 300, the Greek calendar was superseded by the Roman calendar, and since the dates of the beginnings and endings of the months in these two systems did not coincide, 14 Artemision became April 6th.With these dates assigned to Jesus' death and conception we get a birthday of December 25 in the West. I think this reasoning is fallacious in several areas, though Chrysostom deriving this date based on John the Baptist's conception is more reasonable. I think Jesus' birth was more likely to have occurred about September. Nevertheless, the article challenges the idea that this date was borrowed from a pagan holiday.
In contrast, second-century Latin Christians in Rome and North Africa appear to have desired to establish the historical date on which the Lord Jesus died. By the time of Tertullian they had concluded that he died on Friday, 25 March 29. (As an aside, I will note that this is impossible: 25 March 29 was not a Friday, and Passover Eve in A.D. 29 did not fall on a Friday and was not on March 25th, or in March at all.)
So in the East we have April 6th, in the West, March 25th. At this point, we have to introduce a belief that seems to have been widespread in Judaism at the time of Christ, but which, as it is nowhere taught in the Bible, has completely fallen from the awareness of Christians. The idea is that of the “integral age” of the great Jewish prophets: the idea that the prophets of Israel died on the same dates as their birth or conception.
Interestingly there is some evidence that the Magi visited Jesus about December 25.