On a July day in 1518, a woman identified in historical records as Frau Troffea stepped into a narrow street in Strasbourg and began to dance. There was no music. She did not stop. She danced for hours, then through the night, and was still dancing the following morning. Within a week, 34 others had joined her. By August, the number had reached approximately 400. Many danced until they collapsed from exhaustion, stroke, or heart failure. Contemporary accounts describe bleeding feet, expressions of terror, and desperate pleas for help—the dancers did not appear to be enjoying themselves. They appeared to be compelled.
The municipal authorities' response is documented in Strasbourg's civic records with unusual thoroughness. Initially, they concluded that the dancers needed to "dance out" their affliction. Guildhalls were opened. A stage was constructed. Musicians were hired to provide accompaniment—a decision that, in retrospect, almost certainly accelerated the contagion. When the crisis deepened, the authorities reversed course: the dance halls were closed, the afflicted were carted to a mountaintop shrine dedicated to Saint Vitus, and religious intercessions were organized.
Modern explanations for the Strasbourg dancing plague fall into three broad categories, each with significant limitations. The first is ergotism—poisoning by ergot, a fungus that infects grain and contains lysergic acid compounds related to LSD. Ergotism can produce convulsions, hallucinations, and involuntary muscle movements. However, it does not typically produce coordinated, rhythmic, sustained movement resembling dance, and the outbreak's geographic concentration (Strasbourg, not the surrounding rural areas where grain was actually grown) argues against a dietary explanation.
The second explanation is mass psychogenic illness (MPI), sometimes called mass hysteria—a phenomenon in which psychological distress manifests as physical symptoms that spread through social observation and suggestion. MPI is well documented in modern contexts: fainting epidemics in schools, twitching outbreaks in factories, episodes of collective tremor. The Strasbourg outbreak occurred during a period of severe famine, smallpox outbreaks, and syphilis epidemics. The population was under extraordinary psychological stress. MPI provides the most parsimonious explanation, though it raises the question of why the specific symptom was dance rather than some other involuntary movement.
The third and most compelling theory, advanced by historian John Waller, integrates the MPI model with the specific cultural context of sixteenth-century Strasbourg. The region's folk tradition held that Saint Vitus had the power to curse people with compulsive dancing. Waller argues that this cultural belief provided a "template" for the expression of distress—people under extreme stress, in a community that believed dancing curses were real, experienced their psychological anguish through the specific idiom their culture made available. The belief did not cause the plague. The stress caused the plague. The belief shaped it.
The Strasbourg dancing plague remains one of the most thoroughly documented instances of mass psychogenic illness in the pre-modern record. It is not an amusing historical curiosity. It is evidence that the boundary between mind and body, between belief and biology, is more permeable than modern medical practice typically acknowledges.