Sol Invictus, the Unconquerable Sun
Question: "Did Christmas originate from a pagan holiday?"
There has been a long tradition among Protestants of accusing Roman Catholics of engaging in pagan practices based on shoddy history, and modern atheists seem to have taken up that tradition in order to discredit Christianity altogether.
The claims that Christmas originated as a pagan festival have a number of problems historically. For one, the Saturnalia, which is often claimed to be the feast that inspired Christmas was celebrated on December 17th, and eventually this feast was expanded to a week, which ended on December 23rd. The feast of the Unconquerable Sun, which actually was celebrated on December 25th, is a much later feast. The earliest evidence that this feast was celebrated on December 25th comes from a text dated in the year 354 a.d. The earliest Christian reference to a belief that Christ was born on December 25th comes from St. Hippolytus' commentary on Daniel, which was written about 150 years earlier. So if anyone was trying to displace a feast, it is more likely that Pagan Romans were trying to displace a Christian feast, then the other way around.
The other problem with this claim is that the Feast of the Annunciation is the more ancient feast. It was believed that the Messiah would complete his earthly mission on the anniversary of its inception. And we find Tertullian stating that Christ was Crucified on March 25th as early as 208 a.d. (An Answer to the Jews, Ch. VIII). If you calculate a birth exactly nine months later, you come to December 25th.
A further problem with this claim is that before Christmas became a universal feast of the Church, most of the Church celebrated Christ's birth and the beginning of his ministry in His baptism on January 6th. Only later, when the eastern part of the Church adopted the celebration of Christmas was the celebration of Christ's birth transferred to that date, and January 6th exclusively focused on Christ's baptism.
But even if it were the case that there was a pagan feast celebrated on December 25th, if Christians had displaced it with a Christian feast, this would hardly make the celebration pagan in origin. To prove that, you would not to demonstrate a lot more than the coincidence of the date.
More wild claims that the idea of the virgin birth of Christ is based on pagan myths have even less historical credibility. For the most part they are based on made up similarities that have no actual basis in reality.
For more information:
The 25th of December Pagan Feast or Patristic Tradition?", by Hugh O'Donnell
"Why December 25?" by Jon Sorensen
"Was the Virgin Birth of Jesus Grounded in Paganism?" by Jon Sorensen
"Was the Virgin Birth Story Created by the Church?" by Mikel Del Rosario