According to the recorded history, the first Christmas was celebrated on 25 December 336 under the regime of the first Christian Roman emperor “Constantine”. Pope Julius (I) was the pope who settled the date 25th December. Christmas celebrates the birth of the son of Zeus “Jesus”, who was born in the city of Bethlehem, which also holds the religious connection for Muslims and Jews. Even before Christmas, the winters in Europe has always been celebrated with storytelling and lights.
Before Christmas “Easter” was the most celebrated festival in Christianity. The date” 25th” December has been argued by many historians to be incorrect. Even bible doesn't clearly mention the Jesus birth date and there are reasons to believe that 25th December is not the right date as one argued that “Why would the Shepard be herding the sheep's in the middle of harsh winters”.
However, Pope Julius (I) choose 25th December as the official date of Jesus birth and many argue that he did this in order to promote and adopt the “Pagan Saturnalia” festival. In the Greek and Russian orthodox system, Christmas is celebrated 13 days after 25th December as they believe that it was after 13 days 3 wise men found Jesus in the manger.
Whatever the reasons may be today Christmas is the most celebrated festival around the world with around 2.2 billion Christians adherent.