Pre-Christian winter festivals
A winter festival was traditionally the most popular festival of the year in many cultures. Reasons included less agricultural work needing to be done during the winter, as well as people expecting longer days and shorter nights after the winter solstice in the Northern Hemisphere. In part, the Christmas celebration was created by the early Church in order to entice pagan Romans to convert to Christianity without losing their own winter celebrations.
 Most of the most important gods in the religions of Ishtar and Mithra had their birthdays on December 25. Various traditions are considered to have been syncretised from various winter festivals. Christian celebration
Origen, a father of the Christian church, argued against the celebration of birthdays, including the birth of Christ.
It is unknown exactly when or why December 25 became associated with Jesus' birth. The New Testament does not give a specific date.
 Sextus Julius Africanus popularized the idea that Jesus was born on December 25 in his Chronographiai, a reference book for Christians written in AD 221. This date is nine months after the traditional date of the Incarnation (March 25), now celebrated as the Feast of the Annunciation. March 25 was considered to be the date of the vernal equinox and therefore the creation of Adam; early Christians believed this was also the date Jesus was crucified. The Christian idea that Jesus was conceived on the same date that he died on the cross is consistent with a Jewish belief that a prophet lived an integral number of years.
The identification of the birth date of Jesus did not at first inspire feasting or celebration. Tertullian does not mention it as a major feast day in the Church of Roman Africa. In 245, the theologian Origen denounced the idea of celebrating Jesus' birthday "as if he were a king pharaoh." He contended that only sinners, not saints, celebrated their birthdays.
The earliest reference to the celebration of Christmas is in the Calendar of Filocalus, an illuminated manuscript compiled in Rome in 354. In the east, meanwhile, Christians celebrated the birth of Jesus as part of Epiphany (January 6), although this festival focused on the baptism of Jesus.
Christmas was promoted in the east as part of the revival of Catholicism following the death of the pro-Arian Emperor Valens at the Battle of Adrianople in 378. The feast was introduced to Constantinople in 379, to Antioch in about 380, and to Alexandria in about 430. Christmas was especially controversial in 4th century Constantinople, being the "fortress of Arianism," as Edward Gibbon described it. The feast disappeared after Gregory of Nazianzus resigned as bishop in 381, although it was reintroduced by John Chrysostom in about 400.