Celebrating Christmas On December 25 Started With The Pagans
Although Dec. 25 is celebrated as the birthday of Jesus, the Bible doesn’t actually say when Christ was born. In fact, context from the Gospels suggests that it’s more likely the actual date fell in the spring or autumn.

Public DomainThe Adoration of the Magi, a 15th-century painting by Giovanni di Paolo.
So, why do we celebrate Christmas in December? It may all go back to Saturnalia.
Under the reign of Emperor Constantine (306 C.E. to 337 C.E.), Christianity spread throughout the Roman Empire. In 336, the Church officially began observing Christmas on Dec. 25 — perhaps so that it would weaken Saturnalia festivities and the pagan beliefs that went along with them.

Public DomainSaturnalia was observed between Dec. 17 and 23 to celebrate the winter solstice.
Constantine wanted Rome to leave paganism behind and adopt Christianity as its official religion. Introducing a Christian holiday that would be celebrated at the same time as Saturnalia allowed the pagan festival to gradually be absorbed into Christmas. Its decorations and traditions were co-opted, but the symbolism behind them was changed into something more biblical.
