The Roman Emperor Aurelian established a feast of the birth of Sol Invictus (the Unconquered Sun), on this date in 274 CE. The move elevated the Sun God to a higher status among the divinities of Rome (which, of course, elevated the Sun God’s priesthood as well). Sol Invictus would be a popular god, considered a protector of soldiers, and within fifty years, Constantine I would declare dies Solis, Sunday, to be the Roman day of rest. The coincidence with Christmas led 18th– and 19th-century scholars of religion to speculate that December 25th had been chosen as the birthdate of Jesus of Nazareth in an effort to co-opt the pagan holiday. More contemporary scholars note that December 25th comes nine months after March 25th, the date of the vernal equinox, on which the Annunciation, that is, Mary’s pregnancy, was celebrated. Images of the Sun God appear among the decorations in several ancient synagogues in Israel and other lands.
“The notion that creation and redemption should occur at the same time of year is also reflected in ancient Jewish tradition, recorded in the Talmud. The Babylonian Talmud preserves a dispute between two early-second-century C.E. rabbis who share this view, but disagree on the date: Rabbi Eliezer states: “In Nisan the world was created; in Nisan the Patriarchs were born; on Passover Isaac was born… and in Nisan they [our ancestors] will be redeemed in time to come.” (The other rabbi, Joshua, dates these same events to the month of Tishri.) Thus, the dates of Christmas and Epiphany may well have resulted from Christian theological reflection on such chronologies: Jesus would have been conceived on the same date he died, and born nine months later.” —Andrew McGowan, Bible History Daily