As is tradition, the self appointed smartest people in the room have begun their usual, self-congratulatory pronouncements that Christmas is really a pagan holiday, probably Saturnalia.
All of this is hogwash. And Fr. Dwight Longenecker and Dr. Taylor Marshal have all the evidence to back up the traditional date.
I will only add that the dates of Saturnalia (December 17th -December 23rd) are indeed significant in the Traditional Roman Rite: They are days of Penance. While all of Advent has a penitential character (Purple = Penance, people!), these late days before Christmas were especially so. Not only do the Winter Ember Days (days of fasting that occur four times a year) usually occur during those days, but there are no saint days celebrated during this period (save the Feast of St. Thomas on Dec. 21 and, in some places, the Feast of the Expectation of Mary on Dec. 18th).
Once again, we find the Church bidding her children to fast while the world feasts, and feast while the world tries desperately to walk off its hangover.
Blessed Advent, miserable sinners!