Reading from "The Bible as History" by Werner Keller, I found an interesting note regarding the origins of Christmas.
And what about this Roman pagan holiday on December 25?Christendom celebrates Christmas from December 24-25. Astronomers and historians, secular and ecclesiastical, are however unanimous that December 25 is not the authentic dates of the birth of Christ, neither with regards the year nor the day. The responsibility for this lies at the door of the Scythian monk Dionysius Exiguus, who made several mistakes and miscalculations. He live in Rome and in the year 533 he was instructed to fix the beginning of the new era working backwards. But he forgot the year zero which should have been inserted between 1 B.C and 1 A.D. He also overlooked the four years when the Roman emperor Augustus had reigned under his own name, Octavius.The Biblical tradition gives this clear indication" "Now when Jesus was born in Bethlehem of Judaea, in the days of Herod the king ( Matt, 2.1) We know from numerous contemporary sources who Herod was and when he lived and reigned. In 40 B.C. Herod was designed king of Judaea by the Romans. His reign ended with his death in 4 B.C. Jesus must therefore have been born before 4 B.C. if Matthew's statement is correct.December 25 is referred to in documents as Christmas Day in 354 A.D. for the first time. Under the Roman emperor Justinian, it was recognized as an official holiday. An old Roman festival played a major part in the choice of this particular day. December 25 in ancient Rome was the "Dies Natalis Invicti," "the birthday of the unconquered," the day of the winter solstice and at the same time, in Rome, the last day of Saturnalia, which had long since degenerated into a week of unbridled carnival and, therefore, a time when the Christians could feel most safe from persecution.
The Dies Natalis Invicti was probably first celebrated in Rome by order of the Emperor Aurelian (270-5), an ardent worshipper of the Syrian sun-god Baal. With theSol Invictus was identified the figure of Mithra, that strange eastern god whose cult resembled in so many ways the worship of Jesus, and who was at one time a serious rival of the Christ in the minds of thoughtful men.Mithraism resembled Christianity in its monotheistic tendencies, its sacraments, its comparatively high morality, its doctrine of an Intercessor and Redeemer, and its vivid belief in a future life and judgment to come. Moreover Sunday was its holy-day dedicated to the Sun. http://www.worldspirituality.org/december-25.html