With its pageantry, its closeness to nature, its throngs of people celebrating and cramped rooms with blazing fires, the Middle Ages seems perfectly in tune with the spirit of Christmas. Illuminated manuscripts paint a far rosier picture of life in a medieval winter, of course, than it actually was—that was their job—especially if you weren't on good terms with the people in the castle. Even at the manor, life must have been dark, sooty, smelly, fearful, and brief.

And we haven't even come to the demons, goblins, and ghosts that infested every part of life. A thousand quaint superstitions cluster around the mystic season. It is then that the Wild Huntsman sweeps through the air, the powers of evil are loose, werewolves prowl, and witches work their wicked will.

One had to be especially watchful during the twelve days between Christmas and Epiphany. These twelve strange days came from the gap between the short lunar year of twelve months and the longer solar year of 365 days. Epiphany, January 6, was the traditional date on which Christ was baptized. It had originally been his birth date but the church fathers wisely moved it to December 25, the day on which pagan Europe (mistakenly) celebrated the winter solstice.

The twelve lost days of Christmas were a time removed from time itself, a time when the world was turned upside down. Servants became masters, women propositioned men. A mock king was elected, the King of the Bean, along with a Bishop of Fools and an Abbot of Unreason. Boys were crowned pope and donkeys were taken into churches to celebrate mass. A lot of drinking, bonfires, feasting, and bizarre behavior—in other words, a great way to begin the year.

This reversal of normal behavior suggested that the world could have been otherwise arranged, a surprising (but perhaps necessary) concept in a society as rigid as feudalism. And yet the world itself was subject to constant disruptions by unseen forces and by the always unpredictable will of God.

In the 13th century people still lived in a permanent state of awe in the face of divine intervention, and wonder at nature and its mysterious workings. Mistletoe could kill you—as it had the Norse god Balder—and it had magic properties, being of celestial origin. Even if it wasn't the golden bough borne by Aeneas on his journey to the underworld (as I was taught in school), it was still a supernatural plant that grew not with roots in the earth but on an oak bough. Mistletoe was believed to fall out of the sun in a lightning flash on Midsummer's Day. It contained the seed of fire from which the sun itself emanated, and had the power to open any lock and reveal treasures on earth. Given in a drink it rendered any animal fertile and was an antidote for all poisons. Laid on the threshold of a house it prevented nightmares. It was fed as a preventative to the first calves born after New Year's day "for it is well known that there is nothing so harmful to milk and butter as witchcraft." Placed under the pillow of the sleeper it induced omens in dreams.

A thousand years earlier Pliny the Elder, the Roman collector of eccentricities, had bemoaned, while writing about similar beliefs among the Druids: "Great is the power of superstition among most people in regard to relatively unimportant matters." But these superstitions were part of the energetic magic of the Middle Ages, a miraculous way of thinking that imbues paintings of the Nativity with celestial realism. Here in a lowly manager, the convergence of the divine, the fantastic, and the mundane—the Three Wise Men, angels, shepherds, and attendant animals—seem to confirm that the most miraculous event is also the most natural.