Even today, Christmas is celebrated on different dates. Eg in Ireland we have Christmas dinner and present giving on the 25th of December; in many other European countries, Christmas Eve or Epiphany (6th of January) is the important day. And some Orthodox churches celebrate according to the Julian calendar, so in our January.
The Christmas season in Ireland today extends to Epiphany, giving the traditional 12 days of Christmas, or Christmastide. In Ireland, the 6th is called Nollaig na mBán, Women’s Christmas, or Little Christmas.
In Roman times, the winter solstice was on the 25th of December. Symbolically, that made a good date for the birth of Christ, sometimes equated to the sun. Plus it’s conveniently nine months after Easter, which was assumed to be the time he was conceived, related to a Jewish belief that very important people were born and died on the same date, so that their lifetimes were a whole number of years. The date was chosen, and first celebrated, in the 4th century, in Rome.
Epiphany, on the 6th of January, the celebration of the arrival of the Wise Men (Magi), the baptism of Jesus, and in some churches, the birth of Christ, may have been celebrated as early as the 2nd century, but the earliest reference as a feast day is from the 4th century.
Candlemas, on the 2nd of February, the celebration of Jesus being presented at the Temple, used to mark the end of Christmastide. It still marks the end of the Christmas season in some places, such as Puerto Rico. Candlemas was first celebrated in Jerusalem, also in the 4th century, and spread westwards over the next few centuries.
Religious controversy meant that Christmas Day became less important, and Epiphany was the bigger celebration until Charlemagne was crowned the first Holy Roman Emperor on Christmas Day in 800 CE. Later Christmas coronations include Mieszko II Lambert and Bolesław II the Generous of Poland in 1025 and 1076, William the Conqueror in 1066, Roger II of Sicily in 1130, possibly Stephen I of Hungary in 1000, and, according to legend, Edmund of East Anglia in 855. Sweyn Forkbeard, already king of Denmark and Norway, was not crowned in England, but was declared King of England on Christmas Day 1013.
Despite that, various rules were made in the 6th century, forbidding work or fasting on Christmas Day or proclaiming the 12 days of Christmas a sacred and festive season and urging Holy Communion to be taken on the 25th. Saint Augustine is said to have baptised over 10,000 Britons one Christmas Day.
12th Night is still important to us in the SCA. We have a coronation near that date to crown our royal prince and princess as king and queen. The next one will be in Aarnimetsa (Finland). You can learn more about the current heirs on the Drachenwald website.