Happy Saturnalia everybody!
From the History Channel...
In the early years of Christianity, Easter was the main holiday; the birth of Jesus was not celebrated. In the fourth century, church officials decided to institute the birth of Jesus as a holiday.
Unfortunately, the Bible does not mention date for his birth (a fact Puritans later pointed out in order to deny the legitimacy of the celebration). Although some evidence suggests that his birth may have occurred in the spring (why would shepherds be herding in the middle of winter?), Pope Julius I chose December 25. It is commonly believed that the church chose this date in an effort to adopt and absorb the traditions of the pagan Saturnalia festival.
Merry Christmas anyway!