"Celebrating the turn of the year is an ancient custom. The Romans celebrated the Saturnalia, the festival of Saturn, God of harvest, between December 17 and 23. It was the most cheerful festival of the year. All work and commerce stopped, and the streets were filled with crowds and a carnival atmosphere. Slaves were temporarily freed, and the houses were decorated with laurel branches. People visited one another, bringing gifts of wax candles and little clay figurines.
Long before the birth of Christ, the Jews celebrated an eight-day Festival of Lights [at the same season], and it is believed that the Germanic peoples held a great festival not only at midsummer but also at the winter solstice, when they celebrated the rebirth of the sun and honored the great fertility gods Wotan and Freyja, Donar (Thor) and Freyr. Even after the Emperor Constantine (A.D. 306-337) declared Christianity to be Rome's official imperial religion, the evocation of light and fertility as an important component of pre-Christian midwinter celebrations could not be entirely suppressed.
In the year 274 the Roman Emperor Aurelian (A.D 214-275) had established an official cult of the sun-god Mithras, declaring his birthday, December 25, a national holiday. The cult of Mithras, the Aryan god of light, had spread from Persia through Asia Minor to Greece, Rome, and as far as the Germanic lands and Britain.
Numerous ruins of his shrines still testify to the high regard in which this God was held, especially by the Roman legions, as a bringer of fertility, peace and victory.
So it was a clever move when, in the year A.D 354, the Christian church under Pope Liberius (352-366) co-opted the birthday of Mithras and declared December 25 to be the birthday of Jesus Christ"
- NEUE ZURCHER ZEITUNG, Anne-Susanne Rischke, December 25, 1983