Why Do We Celebrate Christmas On December 25?

Ah, Christmas: the most wonderful time of the year, according to Andy Williams and basically every retailer in the Western world. However, as we become lost in all the beauty of the twinkling lights, sparkling ribbons, and spiked eggnog, it can be easy to forget the origins of Christmas. Of course, we all know about the birth of Jesus, but where did our Christmas traditions come from, and why do we celebrate it every year on December 25? We don't even know exactly when Mariah Carey was born. How are we so confident about Jesus?
Was Jesus Born On December 25?
The truth is we can't be totally sure about Jesus' birthday. Despite eventually becoming one of the most popular religions in the world, Christianity started small and faced great persecution, so celebrations of Jesus' birth went undocumented until 336 C.E. That's as far back as we have proof, in the form of an ancient Roman calendar, that it was celebrated on December 25, but three centuries is plenty of time to forget someone's birthday if you neglect to write it down. Most of us forget after three days.
You might assume it has something to do with the scripture, but the Bible is remarkably vague about the time of year when Jesus was born. The obvious thing to do would be to search for documentation of the Star of Bethlehem, which is said to have guided the Magi to Jesus after his birth, but the closest astronomers have found to an event like this occurring was the meeting of Jupiter, Saturn, and the Moon in 6 B.C.E. There's a number of problems with connecting this event to Jesus' birth on December 25: It happened in the spring, not winter, and it's famously believed Jesus was born in the year 0. The Bible gives some evidence, however, that his birth likely occurred closer to springtime, as the mentions of shepherds working the fields would make more sense during spring rather than the dead of winter.

Norse Christmas
The reason for celebrating Jesus' birth on December 25 probably has a lot less to do with the Bible than the patchwork of religions that existed across Europe in the early fourth century, specifically the various pagan religions, almost all of which celebrated the coming of winter as a significant holiday. The Winter Solstice, the day when the Earth is at its greatest tilt and thus experiences the longest night of the year, was especially important to pre-Christian European religions. Winter was always a hard time for people, as survival depended greatly on how much food could be cultivated and stored before the cold and snow took away a good deal of your nutritional opportunities. In plain English, you may starve to death before spring, so you'd better party it up.
The Norse celebration of winter was known as Yule, which the ancient Germanic people celebrated by feasting on the last of their livestock, singing, decorating trees, and drinking ale. Some classic Christmas iconography, like the Yule log and Christmas tree, can be traced back to the evergreen trees that were central to this pagan festival, representing the hope that life could outlast even the cruelest of climates. Not for nothing, but the Norse god Odin was said to zoom across the night sky on an eight-legged horse, which sounds suspiciously close to the modern-day myth of Santa, who has been pulled by eight reindeer ever since the 1823 poem A Visit From St. Nicholas by Clement Clarke Moore.

Pagans And Saturn
The generally accepted theory by most historians regarding the celebration of Christmas on December 25 is that the Romans, in their efforts to Christianize various pagan religions, essentially embraced their traditions while also rebranding them. This tactic can be seen even more clearly in Halloween, which has its roots in the Celtic traditions of harvest festivals that honored the dead and Christians renamed All Hallow's Eve in honor of their own deceased saints.
The Romans may have even stolen from themselves when it comes to Christmas, as there are likewise similarities between the Christian holiday and the ancient Roman celebration of Saturnalia, which honored the god of wealth and renewal. Every year in December, Romans exchanged gifts, lit candles, and treated each other with greater kindness and care despite social standing, hoping Saturn would reward them with a bountiful harvest in the coming year (the god, not the planet).

Winter Sun Gods
For all the European pagan influences on the symbolism and traditions of Christmas, we may need to revisit the Middle East to find a concrete answer to the December 25 question, specially the ancient Iranian sun god Mithra. This god, who was well known to the Roman Empire prior to the rise of Christianity in the fourth century, had a similarly miraculous birth, said to be born from rock. Over time, the myth was reworked into the Roman Mithraic mystery, a secretive religion which honored the god. In Rome, this morphed into Sol Invictus, to whom a temple was dedicated on December 25, 247 B.C.E. A festival in Sol's honor was also said to have taken place on December 25.
As Christian influence took over Rome, many saw Jesus as the true embodiment of the sun god and thus perhaps appropriated this day of commemoration as his birth date. In a way, this afforded tolerance to the older religions while also creating a cultural pathway towards monotheism, specifically Christianity, without the use of domination or violence. After all, who needs spears and swords when you can incorporate and assimilate?

Christmas In Recent Years
The pagan roots of Christmas ironically turned many Christians off the holiday in the centuries that followed. In the American colonies, for example, many Puritans disdained and even banned Christmas celebrations due to its so-called heathen roots. It wasn't until the great American writer Washington Irving, known best for Sleepy Hollow, wrote a satire of Saint Nicholas called History Of New York in 1809 that the holiday spirit truly kicked off in the States.
The 19th century was the birth of Christmas as we know it today, with books like A Christmas Carol bursting into the mainstream in 1843 and cartoons from Thomas Nast in the 1860s burning the image of a red-suited, jolly, fat Santa Claus into the minds of the American public ever since. By that decade, businesses had figured out how to make money off the day by selling decorations and children's toys, and the United States finally made Christmas a nationally observed holiday on June 26, 1870.
So was Jesus born on December 25? Probably not, but that doesn't make Christmas any less important or less meaningful to those who celebrate.