Christmas Day is a Christian holiday commemorating the birth of Jesus Christ. Although the actual date of Christ's birth is unknown, it has been celebrated on December 25 since the 4th century. Christmas is also extensively celebrated by non-Christians as a seasonal holiday, on which popular traditions such as gift-giving, feasting, and caroling take place.
In ancient times, Celts divided the year into four sections marked by "quarter days" -- the days of the two solstices and two equinoxes. The winter solstice, the shortest and darkest day of the year, was the fourth quarter day. It signaled a celebratory time, as the Sun began to reemerge and the land experienced a rebirth. Gradually, to conform more closely to the liturgical year of the Christian church, the fourth quarter day merged easily with the Christian celebration of the birth of Christ. As Christianity began to spread in the 4th century, the Christmas feast day was set on December 25 by Pope Julius I to align with the Roman pagan holiday Dies natalis solis invicti, "the birth of the invincible Sun."
Today's rich mosaic of Christmas customs dates back through the ages. Evergreen branches were used to symbolize life in ancient solstice festivals, as they stayed green in winter. This tradition was absorbed by Christians, who interpreted the evergreens as the Paradise tree and began decorating them with apples. The candles and lights associated with Christmas, meant to symbolize guiding beacons for the Christ child, may have evolved from the Yule log, which was lit to entice the Sun to return as part of the jol (Yule) festival in pagan Scandinavia.