In July 1518, Frau Troffea began dancing in a Strasbourg street and could not stop; within a week dozens joined, within a month reportedly hundreds, dancing for days without rest until September, some dying of strokes and exhaustion, per chronicles kept in Latin and High German. The city prescribed dancing, clearing a guildhall, hiring musicians and strong men to dance the afflicted through it, and later shipped sufferers to the shrine of St. Vitus. It was the last and best-documented of a series of outbreaks along the Rhine running back to the 1370s.
The popular modern explanation, ergot, the hallucinogenic rye fungus, fails on the symptoms: ergot causes convulsions, burning extremities, and gangrene, St. Anthony's Fire, and nobody poisoned by it could dance for days; Strasbourg reported no fire cases that year. Paracelsus, visiting in 1526, offered the first psychological reading, and blamed Troffea for faking it to spite her husband. John Waller's account, the accepted one: mass psychogenic illness, a population broken by famine, smallpox, and the English sweat, in a culture taught that St. Vitus cursed the unrepentant to dance.
The claim: the dancing plagues are the pre-print proof that behavior is contagious below the level of choice, the 1962 Tanganyika laughter epidemic, the 2011 Le Roy tics, every viral challenge since, run the same protocol: stress, suggestion, an audience, and a body that follows. Verdict: the mechanism is documented across five centuries and three continents. The archive's note: Strasbourg's cure, give them a stage and musicians, is the platform business model. The city amplified the dance to end it. It worked then. It monetizes now.
If the cure they prescribed was more dancing, who was treating whom?