text: why is christmas celebrated in december? jesus was not born in december it is a fact. then why do christians celebrate jesus's birth in december? this date was chosen to coincide with the roman festival marking the birthday of the unconquered sun. (the new encyclopedia britannica) pagans held ceremonies to get this source of warmth and light to come back from its distant travels. december 25 was thought to be the day that the sun began its return. in an effort to convert pagans, religious leaders adopted this festival and tried to make it seem "christian."