On June 24, 1374, a bizarre and mysterious phenomenon swept through the town of Aix-la-Chapelle, Germany—a sudden outbreak of “dancing mania.” Also known as “St. John’s Dance,” this strange affliction saw people compulsively break into wild, frenzied dancing that could last for hours, even days, until they collapsed from sheer exhaustion. The cause of this unusual epidemic remains a mystery, but the mania quickly spread across Europe, affecting towns in Italy, Luxembourg, and France.

The dancing fever seemed highly contagious, overtaking entire communities. Men, women, and even children were seen dancing uncontrollably in the streets, unable to stop. As the plague spread, reports of mass hysteria and frenzied movements created widespread panic. While some believe this outbreak may have had physiological roots—possibly caused by ergot poisoning from moldy rye bread—others suggest it was a sociological response to the extreme stress and fear of the time, a form of mass psychosis.

Dancing mania of 1374 remains one of history’s strangest and most perplexing phenomena, leaving historians and medical experts intrigued by the possible causes behind this unusual medieval plague.