It’s not what you think:
Christmas on December 25 is NOT due to there being a pagan holiday on that day. Repeat: Christmas is NOT based on the Roman festival of Sol Invictus. Substantial scholarship has shot down that theory, but we keep hearing it–in the press, in books that try to debunk Christianity [From Cranach: Why December 25 is Christmas]
A new report from Biblical Archaeology Review ought to put that myth to rest forever.