In July 1518, a woman named Frau Troffea stepped into a narrow street in Strasbourg — then part of the Holy Roman Empire — and began to dance.
She danced without music. She danced without apparent joy. She danced the way a person dances who cannot stop, whose body has been seized by a rhythm that has nothing to do with pleasure and everything to do with compulsion. Her feet moved and kept moving. Her arms moved. Her face, witnesses said, was not the face of a woman enjoying herself.
She danced for most of a week.
By the time she stopped — by the time she was taken somewhere and restrained — as many as thirty-four others had joined her. They had not chosen to. They had simply, one by one, begun to move in the same helpless, rhythmic way and found they could not stop.
Within a month, the number had grown to approximately four hundred.
Some of them danced themselves to death.
What Happened in Strasbourg
The Dancing Plague of 1518 is documented in enough contemporaneous sources — physician notes, local chronicle entries, church records, a municipal order — that its basic reality is not in question. Something happened in Strasbourg in the summer of 1518. Four hundred people, over the course of approximately two months, were seized by an uncontrollable urge to dance that many of them could not stop and that killed some of them through heart failure, stroke, and sheer exhaustion.
The municipal authorities of Strasbourg, to their credit, attempted to manage the crisis. Their response is one of the most remarkable documents of the period: they hired musicians and professional dancers to accompany the afflicted, on the theory that the dancing would be safer if performed in a controlled space with proper musical accompaniment. They cleared the grain market and two other large halls. They provided a stage.
This made it worse. The dancing spread further.
The musicians were dismissed. The halls were closed. The afflicted were loaded onto carts and taken to a shrine to St. Vitus — the patron saint of dancing — in the hills above the city, where priests conducted religious rituals over them.
By September, the outbreak had ended. Nobody was dancing anymore. Nobody could explain why.
The Medical Response of 1518
Strasbourg's physicians examined the dancers and produced a diagnosis. They concluded that the dancing was caused by "hot blood" — a concept consistent with the humoral theory of medicine dominant at the time, which held that the body's four humours (blood, phlegm, black bile, yellow bile) could become imbalanced and produce physical and psychological symptoms.
Hot blood, in the humoral framework, produced feverishness, agitation, and uncontrolled movement. The prescribed treatment was exactly what the city authorities ordered: more activity. Dance it out. Let the blood cool through movement.
We can forgive the physicians of 1518 their diagnosis. What is harder to account for is that the treatment — more dancing, in a cleared hall, with professional musicians — is almost certainly what accelerated the spread of the outbreak. By creating a spectacle and a gathering place, Strasbourg's authorities likely increased the number of people exposed to the social contagion mechanism that was probably driving the plague in the first place.
In 1518, nobody had a framework for understanding mass psychogenic illness. They were doing their best.
The Modern Explanation
The most widely accepted modern explanation for the Dancing Plague of 1518 is mass psychogenic illness, sometimes called mass hysteria — a condition in which shared psychological stress manifests as shared physical symptoms across a group of people, spreading through social contagion rather than biological infection.
The framework is well-established. Mass psychogenic illness has been documented in numerous historical and contemporary cases: the Salem witch trials of 1692, in which accusers and accused showed physical symptoms consistent with shared psychological distress; a 1962 outbreak in a Tanzanian school in which laughter spread contagiously and could not be stopped; multiple documented cases in factories, schools, and communities in which physical symptoms — rashes, vomiting, fainting, tremors — spread through groups without any identifiable physical cause.
The Strasbourg case fits this pattern, with one important additional element: the historical context.
In the summer of 1518, Strasbourg was experiencing significant social stress. There had been a famine. There was disease. The political and religious upheaval that would shortly become the Protestant Reformation was building beneath the surface of daily life. The population was living with a sustained level of fear and helplessness that created exactly the conditions in which mass psychogenic illness tends to emerge.
Frau Troffea, in this reading, was not a patient zero in any medical sense but a spark — a person whose breakdown under social pressure provided an unconscious template that spread through a community already primed to receive it.
What This Explanation Does Not Resolve
The mass psychogenic illness explanation is the best one we have. It is not, however, a complete one.
What it does not fully explain is the physiological mechanism by which a psychological state produces uncontrollable movement sustained over days and weeks. The dancers were not choosing to dance. They were not pretending. Some of them begged to be restrained. Some of them beat their feet bloody against the cobblestones and could not stop.
Mass psychogenic illness typically produces symptoms that resolve within hours or days when the affected person is removed from the social environment driving the contagion. Some of the Strasbourg dancers had been dancing for weeks before they stopped. The duration and severity of the Strasbourg outbreak is at the extreme end of documented cases.
The deaths — which period sources number between fifteen and possibly many more — are also difficult to account for fully. People have died in mass psychogenic events, but the Strasbourg case, if the death toll accounts are accurate, represents an exceptionally lethal instance.
Other Dancing Plagues
The Strasbourg outbreak is the most famous, but it is not unique. Historian John Waller, who has written the most thorough modern account of the event, has documented similar outbreaks across the medieval and early modern period — in 1021, 1247, 1278, 1374, and 1381, among others — spread across Germany, Belgium, and the Netherlands.
The 1374 outbreak was particularly significant. It spread across the Rhine valley and affected communities across a wide geographic area. Participants were described as dancing in groups through streets and across fields, often calling out to saints and behaving in ways that suggested profound religious terror alongside the physical compulsion.
The clustering of these events in the medieval period — and their effective disappearance afterward — suggests that specific historical and social conditions were necessary to produce them. As literacy increased, as medicine developed, as the social frameworks for understanding and responding to collective stress evolved, the dancing plagues stopped happening.
But they happened. Repeatedly. For centuries.
In 1518, in Strasbourg, something swept through four hundred people and moved their bodies against their will until it was done with them. Whatever that something was — social contagion, religious terror, mass grief finding a physical expression — it was real. It was devastating. And it has never been fully explained.
The street where Frau Troffea first began to dance is still there. The city built over it. The city grew around it. The dancers were forgotten for centuries until historians went looking for them.
They were real. They danced. Some of them died.
And we still cannot say exactly why.
Sources and Further Reading: John Waller's A Time to Dance, a Time to Die (2008) is the definitive modern account of the 1518 outbreak, based on extensive archival research in Strasbourg and German historical records. The municipal order authorising musicians and a dance space is preserved in Strasbourg city archives. The broader history of mass psychogenic illness is comprehensively documented in Robert Bartholomew and Simon Wessely's Panic Attacks: Media Manipulation, Delusions and Mass Hysteria (2002).