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On this day in 1374, the town of Aachen, Germany, went wild.

Men, women, and children gathered in the streets. They writhed and leaped and twirled, often hand in hand. They screamed, they wept, they cursed, they prayed. But mostly, they moved. This continued for hours—even days—a wholly put-upon rave. Their bodies were bruised, their feet were bleeding, and still they danced, as if in a trance. It ended only when exhaustion won and participants collapsed.

This was the first (and worst) major outbreak of choreomania, the dancing plague, one of the earliest recorded forms of mass psychogenic illness. The people compulsively danced themselves nearly to death—and we still don’t know why.

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This particular number was called St. John’s dance (because June 24 is the feast day of St. John the Baptist). But earlier and later outbreaks were also recorded in other parts of Germany, plus Belgium, the Netherlands, Italy, and France.

Fun Fact

In the French outbreak officials first tried to help by providing professional musicians to accompany the dancers.

Many of the places and participants believed it was the Devil’s doing (some priests threw holy water on dancers to try and exorcise them). In Italy it was thought to have been caused by spider bites. Some modern historians have attributed it to ergot, a fungus that affects rye and can produce effects similar to ingesting LSD. But many outbreaks occurred in the dry season, when ergot would not have been an issue.

The actual cause remains unknown. But what is known is that the people of Aachen (and many of the other affected places) were having a really bad year. We’re talking dealing with the aftermath of the literal plague, total crop failure, and massive flooding (up to 34 feet of river overflow) that resulted in widespread famine and poverty.

Many researchers now believe that the most likely explanation is that the population suffered a shared psychological breakdown, a sort of collective dissociated state. It affected thousands.

No outbreaks of choreomania have been reported since the mid-1600s. Phew.

By the Numbers
  • 400: Dancers in the 1518 Strasbourg outbreak
  • ~25 million: Deaths in Europe from the bubonic plague
  • 7th century: Earliest reported outbreak of dancing plague
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