In July 1518, residents of the city of Strasbourg (then part of the Holy Roman Empire) were struck by a sudden and seemingly uncontrollable urge to dance. The hysteria kicked off when a woman known as Frau Troffea stepped into the street and began to silently twist, twirl and shake.

She kept up her solo dance-a-thon for nearly a week, and before long, some three-dozen other Strasbourgeois had joined in. By August, the dancing epidemic had claimed as many as 400 victims. With no other explanation for the phenomenon, local physicians blamed it on “hot blood” and suggested the afflicted simply gyrate the fever away.

A stage was constructed and professional dancers were brought in. The town even hired a band to provide backing music, but it wasn’t long before the marathon started to take its toll. Many dancers collapsed from sheer exhaustion. Some even died from strokes and heart attacks. The strange episode didn’t end until September, when the dancers were whisked away to a mountaintop shrine to pray for absolution.

The Strasbourg dancing plague might sound like the stuff of legend, but it’s well documented in 16th-century historical records. It’s also not the only known incident of its kind. Similar manias took place in Switzerland, Germany and Holland, though few were as large—or deadly—as the one triggered in 1518.

What could have led people to dance themselves to death?

According to historian John Waller, the explanation most likely concerns St. Vitus, a Catholic saint who pious 16th-century Europeans believed had the power to curse people with a dancing plague. When combined with the horrors of disease and famine, both of which were tearing through Strasbourg in 1518, the St. Vitus superstition may have triggered a stress-induced hysteria that took hold of much of the city.

Other theories have suggested the dancers were members of a religious cult, or even that they accidentally ingested ergot, a toxic mold that grows on damp rye and produces spasms and hallucinations.