In July of 1518, in the city of Strasbourg on the Rhine, a woman later named Frau Troffea stepped into the narrow street and began to dance. That in itself was not remarkable. What made it remarkable was that she did not stop. She danced through the day and into the night, and the next morning she was still dancing, her face drained, her feet raw. Within a week, around thirty people had joined her. Within a month, the number had grown to roughly four hundred, and the authorities had begun to understand that they were watching something they could not explain.
The city fathers responded the way officials of the time knew how. They called in physicians, who examined the dancers and—with no fever, no rash, nothing visible to blame—concluded that the cause was "hot blood" and prescribed the standard cure: more dancing, to sweat the sickness out. Following that advice, the town built a wooden stage in the grain market and hired musicians to play. It was, by every account, a disaster. The music drew more people into the dance, and the dancing went on, day and night, for weeks. Historical accounts record that some of the dancers collapsed and died—sources speak of a dozen or more fatalities—while others danced until their shoes were gone and their feet were bloody.
This was not an isolated incident. Strasbourg was the most famous episode of a recurring phenomenon known across medieval Europe as dancing mania, or the dance of Saint John. In Italy it appeared as tarantism, a frenzied dance believed to be caused by the bite of a spider. Whole villages were sometimes caught in it, and it could flare up, fade, and return for generations.
What caused it? For centuries the most popular theory pointed to ergot, a fungus that grows on damp rye and produces a toxin that can cause convulsions, hallucinations, and a burning sensation in the limbs. Ergot poisoning, it was argued, could have made people twitch and writhe in ways that looked like dancing. But modern researchers have largely moved away from that explanation, because ergotism does not usually spread from person to person, and it does not produce coordinated, rhythmic movement in a crowd.
Today the explanation most often given is mass psychogenic illness—a collective response to stress. Strasbourg in 1518 was a city in crisis: a poor harvest the year before had left people hungry, disease was never far away, and the hot summer pressed on everyone's nerves. When one woman began to dance, the theory goes, the town's shared dread found a physical outlet, and the behavior spread the way a rumor does, through watching and copying. The mind, it turns out, is contagious.
The dancing did not end all at once. The authorities, as a last resort, had the dancers loaded onto wagons and carried to a shrine of Saint Vitus outside the city, where, according to the chroniclers, the frenzy finally released them. Even then, outbreaks continued to flare in neighboring towns through the rest of the summer, and dancing mania would return to the region again and again for the next century and more. Whatever seized the people of Strasbourg was not a single night of delirium. It was a condition of an entire age, ready to wake whenever hunger and dread piled high enough.
Nobody can say with certainty what happened in that street. What survives is a reminder that a crowd is not just many individuals standing near one another; it is a single living thing, capable of sharing a mood, a fear, even a movement, so completely that hundreds of people can do the same inexplicable thing at the same time. If a whole town could fall into step with one woman in 1518, it is not so strange to think that a memory, a story, or a way of seeing the world could pass through a community and keep moving for a thousand years.
The dancers of Strasbourg have been silent for five centuries. But the question they left behind is still moving: how much of what we do is ours alone, and how much is a rhythm we caught from the people around us, without ever knowing when the music started?
Author note: This is a retelling of a well-documented historical event with no settled scientific explanation. The theories above are presented as possibilities, not conclusions.