“Christmas,” the word, comes from the Old English Crīstesmæsse, or literally, “Christ’s Mass” and is festival commemorating the birth of Jesus Christ, now observed on December 25. It closes the period of Advent and begins the 12 days of Christmastide, which end after twelfth night.
The first recorded date of Christmas being celebrated on December 25th was in 336AD, during the time of the Roman emperor Constantine, the first Christian emperor. A few years later, Pope Julius I officially declared that the birth of Jesus would be celebrated on the 25th of December.
Actually, Christ was probably born in the fall of the year. It has been mistakenly believed He was born around the beginning of winter, but according to the Adam Clarke Commentary, it was the Jewish custom to send out their sheep to the deserts at the time of Passover in early spring and bring them home when the first rains began, in in early-to-mid fall. Shepherds watched over them during this time. Since the shepherds had not yet brought their flocks home at the time of Christ’s birth, the event had to have happened sometime in late September. From Luke 2:8: “And there were in the same country shepherds abiding in the field, keeping watch over their flock by night.”
So how did Christ’s birth come to be celebrated on December 25? This date was chosen because it roughly coincided with various Roman festivals. First there was the idolatrous festival of Saturnalia, a time of merrymaking and exchanging of gifts in early Rome. This occurred each year around the beginning of winter, or the winter solstice, when the sun takes its lowest path across the sky and the days begin to lengthen, assuring another season of growth. Saturnalia, of course, celebrated Saturn—the fire god, and also the god of sowing. Saturn was worshipped in this dead-of-winter festival so he would come back to warm the earth for spring planting. Some of the trappings of the Saturnalia parallel what so many of us do today to celebrate Christmas: decorating homes with greenery, giving gifts, singing songs, and eating special foods.
Some Romans worshiped the god Mithra, first found in the Indian Vedic religion as Mitra, 3500 years before the birth of Christ. Interestingly, the Indian Mirta is also a solar deity, being the light and power behind the sun. Mithra was believed to come from a virgin birth, like Christ, and thought by many to have been born on December 25. However, there is no evidence to support this.
In fact, December 25 was considered the birth date of Sol Invictus, literally the “unconquered sun.” Sol Invictus was the official sun god of the later Roman Empire and a patron of soldiers. In 274, the emperor Aurelian made the cult of Sol Invictus one of the traditional Roman cults.
For the past two hundred years, it has been generally thought December 25 was chosen for Christmas in order to correspond with the Roman festivals of Saturnalia, Sol Invictus or the birth of Mithra, in order to convince Rome’s pagan citizens to accept Christianity as the empire’s official religion and to promote the church’s identification of God’s son with the celestial sun.