Christianity - a literal cover-up

You'd think that people out to overwrite one religious system with another would have more imagination, but I guess not. On a lark tonight, I looked up Saturnalia, and looky what I find:

In the Julian calendar, the Saturnalia took place on Dec. 17; it was preceded by the Consualia (Dec. 15) and followed by the Opalia (Dec. 19). The celebrations typically lasted for a week (Dec. 17-23), ending just before the (late imperial) festival for Sol Invictus (Unconquered Sun) on Dec. 25 (the Solstice in the pre-Julian calendar). What is it that the Christians call their central religious figure? and the date they chose to assign to his birth date?

http://www.cs.utk.edu/~mclennan/BA/Saturnalia.html