Sextus Julius Africanus popularized the idea that Jesus was born on December 25 in his Chronographiai, a reference book for Christians written in 221.[15] This date is nine months after the traditional date of the Incarnation (March 25), now celebrated as the Feast of the Annunciation.[19] March 25 was also considered to be the date of the vernal equinox and therefore the creation of Adam.[19] Early Christians believed it was the date Jesus was crucified.[19] The idea that Jesus was conceived on the same date that he died is consistent with a Jewish belief that a prophet lived an integral number of years.[19]
The identification of the birthdate of Jesus did not at first inspire feasting or celebration. 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.[7]
The earliest reference to the celebration of Christmas is in the Calendar of Filocalus, an illuminated manuscript compiled in Rome in 354.[3][20] A reference from 360 indicates that Christmas was well-established in Rome by that time. Christmas was promoted in the east as part of the revival of Trinitarian Christianity following the death of the pro-Arian Emperor Valens at the Battle of Adrianople in 378. It was introduced to Constantinople in 379, to Antioch in about 380, and to Alexandria in about 430. Christmas was especially controversial in Constantinople, 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.[3]
