The story of Christmas
The source and history of Christmas is long and quite varied. Although steeped in religious ceremony, it does not wholly come from the birth of Christ. The name Christmas comes from the "Christ's Mass", as a celebration of the birth of Jesus Christ, but the wintertime holiday has evolved over many centuries. The holiday as we celebrate it in the United States today comes from agricultural, paegan and Christian celebrations from many different countries and cultures.
Traditionally, Christmas is celebrated on the 25th of December, however the Mesopotamian are also known to throw their winter feast at the same time -- 4000 years ago before now and many centuries before the birth of Christ. Also not coincidentally, their celebration stretched to twelve long days of gaiety, not unlike our fabled "12 days of Christmas".
The birth of the ancient sun-god Attis in Phrygia was celebrated on December 25th, as was the birth of the Persian sun-god, Mithras. The Romans celebrated Saturnalia, a festival dedicated to Saturn, the god of peace and plenty, that ran from the 17th to 24th of December. People decorated their villages with flowers and gifts and candles were exchanged among the revelers.
Europeans traditions centered around the winter solstice are have also been folded into our modern Christmas celebration. In Scandinavia darkness ruled the winter days. Upon the first sign of light the people would light a "yule log" in thanks. Similarly, the Celts decorated their homes with evergreen boughs, mistletoe and holly to encourage fertility in the cold months.
The day was not marked as a celebration for Christ's birth until many years after His death. In 137 AD the Bishop of Rome ordered the birthday of the Christ Child celebrated as a solemn feast. In 350 AD another Bishop of Rome, Julius I, choose December 25th as the observance of Christmas.
Even the origination of Santa Claus is a bit controversial. He is known around the world as everything from Santa Calus to Father Christmas, St Nicholas to Pere Noel. The current jolly old man with white whiskers seems to be an amalgam of many kindly, older men usually of Christian religious service (bishops, priests or saints) who share wisdom and generous gifts.