For the first two centuries of Christianity Christmas was not celebrated at all, then several dates came and went 20th May, 19th April, 20th April, but these dates didn’t catch on. Then a group of Egyptian Gnostics called the Basilideans, decided that the day of Jesus’ baptism was the day when he was manifest to the world as the God incarnate, and started to celebrate that day, 6th January. This was indeed seen by the Gnostics as the Epiphany, but they were celebrating Christ’s baptism not the arrival of the Magi. Other Egyptians who had converted from the old Egyptian religion to Christianity were used to celebrating 6th of January as the festival of the virgin-goddess Kore, and soon adopted the 6th of January not only as the a celebration of Jesus’ Baptism, but also of his birth.The date of Christ’s birth continued to be disputed due to the tradition that all biblical characters lived for whole years, being born and dying on the same day of the year.
It was agreed by many that Jesus had died on the Spring equinox - then believed to be the 25th of March - a date which for many was the day the world itself was created. However the debate then moved to suggesting the date as 28th of March as that was the day God created the sun and the moon, God’s sources of light, and Christ was the Light of the world.
The first person that we know of to suggest the 25th of December as the date of Christ’s birth was Sextus Julius Africanus who believed the moment Christ became incarnate was the moment of his conception and that would have fallen on the date of creation. So on the 25th of March the Angel appeared to Mary and 9 months later, 25th December, Jesus would have been born. However during his time such a date didn’t gain much popularity, but soon that was to change.
The main problem was over the 6th of January. In the 4th century it Ephraem, a poet, suggested that the arrival of the Magi, symbolised all peoples of the world acknowledging Jesus as God’s Son, was when Christ was manifest, and hence by the middle of the 4th century, Christ’s birth, Christ’s baptism, the wedding at Cana, the feeding of the five thousand and the arrival of the Magi were all linked with the 6th of January.
The Jews alone used a lunar calendar, with dates beginning at nightfall, while the Romans used a solar calendar - with days beginning at sun rise. In the late 4th century it is recorded that those in Rome celebrated Christmas on the day of 25th December, while Christians from Jerusalem travelled to Bethlehem and celebrated the nativity on the evening of the 6th of January. Finally a compromise was reached and by the 6th century Christmas Day was celebrated at midnight on the 24th/25th December.
It was the French in the 6th century that introduced the idea of 12 days of Christmas. They proclaimed all 12 days of Christmas not just the 25th of December should be sacred and a festival. Linking the 25th December - Jesus’ birth, with 6th of January - Jesus’ baptism and make sure the importance of the Manifestation to the Gentiles wasn’t lost, which they understood as being Jesus’ baptism. The French used a solar, not lunar calendar with the first day of Christmas being 25th December the last being 5th January.
It wasn’t until the early Middle Ages the Western Church was using December 25th to celebrate Jesus’ birth, with the arrival of the Magi on the 6th of January marking the Epiphany. While the Eastern Church never adopted December the 25th, and stuck with their original date of the 6th of January.
So if you celebrate the birth of Christ on the 25th of December then Christmas ends today, 5th January, tomorrow is a new season, that of Epiphany.
