Hat tip to Stephen Huebscher for this one!
Here’s a link to an interesting short essay on this topic. The author argues (with some justification) that rather than Christians adapting a pagan holiday to their sacred calendar, pagans co-opted December 25 from Christians. Here’s a teaser paragraph:
It is true that the first evidence of Christians celebrating December 25th as the date of the Lord’s nativity comes from Rome some years after Aurelian, in A.D. 336, but there is evidence from both the Greek East and the Latin West that Christians attempted to figure out the date of Christ’s birth long before they began to celebrate it liturgically, even in the second and third centuries. The evidence indicates, in fact, that the attribution of the date of December 25th was a by-product of attempts to determine when to celebrate his death and resurrection.
I’m considering devoting an episode of the Naked Bible Podcast to this topic. I’m reading through the only two academic books on Christmas origins I know of. We’ll see if I get through the material in time.