Carl Sommer, author of We Look for a Kingdom: The Everyday Lives of the Early Christians, emailed me a few more bits on the dating of Christmas.
You’ll find a couple of interesting articles relating to the December 25 dating of Christmas here and here. I should probably make my interest in this subject clear. I do not believe it is possible to establish the precise date of Jesus’ birth; and, in
many ways, the exact date is probably unimportant. I am, however, interested in refuting the notion that Christmas is some kind of a “pagan” holiday. December 25 was chosen by Christians for Christian reasons, not as a concession to pagan culture. I have no doubt that by the middle of the fourth century December 25 received a new prominence because of the need to counter Sol Invictus, but Christian usage of December 25 clearly predates that time.
Carl’s right. It’s very clear — from Hippolytus, Julius Africanus, and Clement of Alexandria — that some Christians celebrated December 25 from very early times. Nevertheless, it seems there was a strong push at the end of the fourth century to establish the holiday universally and promote its celebration. It’s possible that this push was the Church’s way of addressing a lingering attachment to Sol Invictus. That’s perfectly compatible, of course, with Carl’s contention that Christmas predates Sol Invictus. Carl responded that he and I are in perfect agreement.