On one July day in 1518 a woman kicked off a three-month-long dance marathon, now known as the dancing plague. But what caused this strange phenomenon?

In July of 1518 a woman named Frau Troffea (possibly Trauffea) went into the center of Strasbourg and began twitching and having spasms. These continued until she became exhausted and would start up again after she rested. There is no mention of anyone attempting to intervene as this pattern continued for an entire week. By the end of the week others joined in the macabre dance with about three dozen convulsing in disjointed movements.

Still more people joined in, and seemed to be affected by the dancing mania. By August it is believed that between 50-400 people had taken part in the dancing. The exhaustion of the marathon of dancing took a toll on the dancers, with many collapsing and dying of exhaustion and essentially dancing themselves to death. There are no exact figures on the mortality rate of the dancing plague, although one source from a man passing through claims at least fifteen died a day.

This wouldn’t be the only outbreak of dancing hysteria, nor was it the first of its kind, although it is one of the most well-known. Other instances took place including earlier in 1374 in Germany. During the time, society was still deeply religious, and these “plagues” were considered curses upon individuals and groups, with many believing there was a connection between the uncontrollable dancing and religious or supernatural causes.