When Pope Gregory first sent Latin missionaries to the outer northern wilds of Europe, he instructed them to make it easy for converts. If they were used to gathering on a hilltop somewhere on a certain day, find a saint’s day that might be celebrated by gathering on a hilltop. If they have a spring festival, tell them to do the same things in honor of a saint or of Jesus’s resurrection. Build wooden or stone churches near where their pagan shrines were, since that’s where they are used to going. Try to adapt the culture.
It’s *somewhat* syncretistic, but Gregory seems to have meant not to keep pagan customs alive—-but to be gentle with the process of conversion. Today we might frame it in terms of not forcing people to give up their culture needlessly; it’s embarrassing to think that at one time, “becoming a Christian” in Africa entailed changing your name and dressing like a Victorian, as though Christians could not have native names or live in traditional ways. The adoption of some pagan traditions has confused the meaning of the holiday for everyone, becoming a popular target for debunkers who want to say it’s all about the pagan gods like Helios, Mithras, or Odin. I don’t think that’s true, but it’s obvious that some of these pagan traditions gave us the trappings we’re familiar with in northern Europe and America.
Germanic people had a long tradition of burning a Yule log for 12 days in midwinter. They kept a feast in the darkness after the solstice; they often roasted a whole boar. The boar may have been on the menu because it was a big, tasty animal that could be more easily hunted with spears in deep snow, or it could have had some religious significance, since each of the gods had a totem animal. The boar was the animal of Tiw, the god whose name gave us Tuesday. It was also good eating.
Yule was a celebration of life in the time when winter seemed dark and cold, so they always went out to collect evergreen branches as home decoration. Christmas decorations did not come into the house or hall until Christmas Eve. There may have been a superstition about its being bad luck to bring outdoor, woodsy things into the house. If so, it goes with the general trend that both conquered peoples and suppressed religions end up being associated with hard-to-see things that slip through the woods: brownies, elves, sprites, and so on. But during Christmastide, it was safe. This period lasted from Christmas Eve to Twelfth Night.
Evergreens are the only leaves that still look alive during the coldest winter; it’s the only color in a northern snowscape. They may have had ritual significance in pagan religion, but they were still great decorations. Ivy usually decorated outside the house, and holly inside. Holly, of course, adds the appeal of red berries. Once pagan religion was far enough in the past that it didn’t seem as dangerous, the church accepted holly as a decoration, pointing out that it also had thorns and the berries were red as blood, so they could bring to mind Christ’s death.
Mistletoe is more deeply connected to pagan myths; a dart made of mistletoe killed Balder, the beautiful Norse god. Mistletoe is a parasitic plant that feeds on a host plant, some other kind of tree. Its green leaves allow some photosynthesis, but mostly it’s living off the tree or shrub it has colonized. It appears as a ball of green leaves nesting in the midst of the branches. Celtic druids observed rituals when collecting mistletoe, especially if it grew on an oak. When it was finally allowed into the house in Christian times, it must have still seemed dangerous, leading to the custom of kissing under mistletoe. This custom probably wasn’t around yet in medieval times.
The Holy Thorn Tree at Glastonbury was a type of hawthorn that flowered in the winter. Its white flowers opening near or on Christmas Day led to a legend that it had been planted by Joseph of Arimathea: he set his walking stick there, and it grew and flowered. The tree that grows on the church grounds has been carefully kept alive by taking cutting from it frequently in case the tree dies.
Evergreen branches of the pine sort could have been used to decorate, too. But even in Germany, where the Christmas tree custom seems to have originated, they weren’t bringing a tree into the house yet in medieval times. Many customs that we think of as medieval are actually from the 16th and 17th centuries. The tree’s use in English custom begins with Queen Charlotte, German wife to King George III.