[Adder]

Hmm, I always thought that Christmas co-opted, as it were, Saturnalia which was an ancient Roman festival where the slaves ruled over their masters for a day and gifts were exchanged.
The latter festival mentioned here was never mentioned previously.
As others have said, it makes little difference that Christ's Mass is celebrated when it is, tho there are several who damn it for having incorporated pagan ritual. Never could understand that one...who cares if they did?

[yatros from flatwater]

Who cares? Yeshua (Jesus) strongly objected to the elevation of human traditions over the commandments of the God of Israel (Matt 15:6, quoting Isaiah 29:13). The substitution tradition goes way back to the fall in Eden. Is it something to celebrate?

As far as the origins of Christ's Mass, see the Catholic Encylopedia for a fairly comprehensive discussion of the various pagan contributions