Touchstone has reposted its most popular article, the scholarly treatment by historian William J. Tighe from 2003 about why the birth of Jesus is celebrated on December 25. And, as he definitively shows, it has nothing to do with any pagan festival.
From William J. Tighe via Touchstone Archives: Calculating Christmas:
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.