What is the origin of the Christmas holiday?

The celebration of the birth of Christ began as far back as around 350 AD.  The date was set to December 25 by Pope Julius I of the Roman Catholic Church.  This date was chosen due to the many pagan winter festivals that were celebrated all over Europe at the time.  The Catholic Church had tried for a couple of decades to get the people to stop these festivals but could not.  So instead, they chose to adopt a Christian holiday around the same time to get everyone on their side.  Since then, many of the pagan traditions of these festivals have entered Christianity (e.g. Christmas trees, yule logs, etc.).