On or about July 14, 1518, a woman known to history as Frau Troffea stepped into a street in Strasbourg and began to dance. There was no music. She kept going until she collapsed, and when she had rested she started again. John Waller, the historian who has studied the episode most closely, puts her solo performance at four to six days.
By the end of the first week more than thirty people had joined her. Within a month, according to a Strasbourg family chronicle, the number had reached 400. The dancing continued into late August or early September, in a prosperous trading city on the Rhine that was then a free city of the Holy Roman Empire.
That much is reasonably secure. Almost everything else people repeat about the dancing plague, including how many it killed, deserves a second look.
What the records say
Strasbourg in 1518 is the best documented of all the dancing outbreaks. National Geographic counts six chronicle accounts, and beyond those there are physicians' notes, sermons and the orders of the city council. The essay on the episode in The Public Domain Review draws on the chronicle of the architect Daniel Specklin, on the Imlin family chronicle that supplies the figure of 400, and on council wording attributed to Sebastian Brant, the city's chancellor and the author of The Ship of Fools.
The most vivid personal detail comes from a writer who was not there. The physician and alchemist Paracelsus visited Strasbourg about eight years later and wrote about Frau Troffea with open contempt. In his telling she was no victim at all. She danced to spite her spouse, and her hopping and singing were, in the translation quoted by The Public Domain Review, "most distasteful to her husband." Paracelsus went on to sort dancing mania into three kinds, arising from lust, from imagination and from bodily causes. It is an early attempt at a natural explanation, and also a secondhand account by a man with strong opinions about women.
Even the numbers are soft. Britannica gives as many as 400 dancers. Other summaries of the sources give a range from 50 to 400.
The cure that made it worse
The city's response is the best attested part of the story, and the strangest. The council consulted physicians, who set aside supernatural causes and diagnosed, in the words quoted from the records, "a natural disease" caused by overheated blood. In the medicine of the day that would normally have meant bleeding. Instead the doctors prescribed more dancing, on the theory that the afflicted had to move the fever out of their systems.
So the council cleared guildhalls for the purpose, built platforms in the horse market and the grain market, and paid musicians to play drums, fiddles and pipes. Healthy dancers were hired to keep the sick on their feet.
It did not work. Onlookers appear to have read the public spectacle as proof that a saint's anger was loose in the city, and more people joined in. The council reversed itself. The stages came down, and music and dancing were banned until September. One exception was allowed for respectable weddings and first Masses, where stringed instruments were permitted but citizens were told, on their conscience, "not to use tambourines and drums."
The final measure was religious. The worst cases were sent to the shrine of Saint Vitus at Saverne, in the hills to the northwest. There, by the account in The Public Domain Review, they were placed beneath a carved image of the saint, given small crosses to hold and fitted with red shoes whose soles had been marked with holy water and consecrated oil. Within a week or so the flow of sufferers thinned, and by early September the outbreak was over.
How many died
The figure most often quoted is that at its height the plague killed about fifteen people a day. Waller repeated it in The Lancet in 2009, and it has traveled from there into nearly every popular retelling, sometimes with heart attacks and strokes added as causes of death.
The difficulty is that the figure comes from a later account. Wikipedia's review of the evidence notes that the Strasbourg sources written at the time of the events, the council notes, sermons and chronicles among them, do not give a death count, or even state plainly that anyone died. Waller himself concedes that the final toll is unknown.
Deaths are entirely plausible. People who danced for days in summer, with little food or water, in a year of hunger and disease, were in real danger. But "fifteen a day" is a number without a contemporary witness, and a claim of hundreds dead rests on nothing firmer than multiplication.
The case against ergot
The best known physical explanation is ergot, a fungus that grows on damp rye and produces compounds chemically related to LSD. Bread made from infected grain can cause convulsions, delusions and hallucinations. The idea was put forward in the 1950s by the Swedish pharmacologist Eugene Louis Backman.
Most historians now reject it, and the reasons are practical. Ergot poisoning restricts blood flow to the limbs, and its victims are in no condition to dance for days. There are no reports of gangrene from Strasbourg, though gangrene is a common sign of ergotism. A contaminated harvest would not make hundreds of people respond with the same behavior. And as Waller has pointed out, the outbreaks cluster along the Rhine and Moselle, regions with different climates and crops but shared beliefs.
A plague with a pedigree
Those shared beliefs are the heart of Waller's alternative. Strasbourg was not the first such episode. Tradition places a group of dancers in a churchyard at Kölbigk in Saxony in the 1020s. Dancing children left Erfurt in 1237 or 1247, depending on the source, and some 200 people are said to have danced on a bridge at Maastricht until it gave way. In 1374 a far larger wave began at Aachen and spread through the Rhineland and the Low Countries. Strasbourg itself had an outbreak in 1418.
By 1518 the people of the upper Rhine knew that Saint Vitus could curse sinners with a compulsion to dance. They were also living through failed harvests, smallpox and the recent arrival of syphilis. Waller argues that under such pressure some fell into a trance, and that the trance took the form their culture had prepared for them. The modern term is mass psychogenic illness. The sociologist Robert Bartholomew has offered a different reading, in which the dancers were members of a religious sect performing a ritual. Neither explanation can be tested against the dead.
Waller's version has one point in its favor that the others lack. It explains why the cure worked. A sickness born of the fear of Saint Vitus ended, more or less on schedule, at a shrine in Saverne, with a pair of red shoes.