In the summer of 1518, people in Strasbourg couldn’t seem to stop dancing—some even danced themselves to death.

It all started with one woman, who stepped into the street and began moving uncontrollably. Soon, dozens of other residents followed suit, overcome with the inexplicable urge to hop, jerk, and sway. Within weeks, the outbreak had spread throughout the city, leaving officials, physicians, and religious leaders scrambling to figure out what was happening—and, more importantly, how to make it stop.

Five centuries later, the dancing plague of 1518 remains one of history’s strangest medical mysteries. Historical records confirm that a bizarre episode turned a medieval city into a very unwilling dance floor that summer, but exactly why it happened remains a matter of debate. 

A bizarre outbreak takes hold

The dancing plague began on July 14, 1518, when a woman named Frau Troffea started dancing in Strasbourg, then part of the Holy Roman Empire and now a city in northeastern France. Though her husband begged her to stop, Troffea kept moving as day faded to night, while a crowd of onlookers gathered around to watch. Eventually, she collapsed and fell asleep, but when she awoke the next morning, she resumed her solitary jig. 

Troffea’s uncontrollable dancing, known as choreomania, seemed to be contagious. Dozens of other people were soon gyrating in the streets of Strasbourg and, by late August, as many as 400 individuals had succumbed.

At the time, the leading theory was that St. Vitus, a fourth-century Sicilian martyr believed to punish sinners by making them dance, had cursed the afflicted. Then, once St. Vitus decided his victims had suffered enough, he would relieve them of the curse.

City leaders determined that the best course of action was to keep the dancers dancing, so they cleared the outdoor grain market, built a stage, and hired musicians. They didn’t explain their rationale in any known, surviving documents, so historians don’t know exactly why they did this. But John Waller, associate professor of the history of medicine at Michigan State University and the author of The Dancing Plague: The Strange, True Story of an Extraordinary Illness, suspects they had two reasons: They believed dancing could help people purge physical impurities from their bodies, and they viewed it as a form of penance. 

“If people were believed to have been cursed by God or a saint for some kind of immorality, well, dancing was associated with hedonism and that was fundamentally immoral,” he tells Popular Science. “A way of basically punishing oneself would be to dance to the point of exhaustion and pain and potentially even death. It would make sense with that potential framework.” In other words, from the leaders’ perspective, if dancing was their punishment, let them be punished.

Dancing themselves to death

Regardless of their motives, the authorities’ decision had “very, very clear consequences,” he says. It was a hot summer, and the dancers were likely under the full glare of the sun. They weren’t eating or drinking much, and they weren’t resting. 

“This is certainly going to be extremely dangerous for a large number of people, particularly anybody with any kind of susceptibility to heart attack or stroke,” says Waller.

The historical records are murky on exactly how many people died—one writer claimed as many as 15 per day, at least for a time—but it was enough to make city leaders completely change course. 

“They essentially banned dancing, except for some people in the privacy of their own homes, and then instituted a program of penance and prayer,” says Waller. “They clearly realized that what they’d been doing before was causing harm and I suspect they got the impression that it was making things worse.”

Eventually, the authorities transported the remaining dancers to a shrine dedicated to St. Vitus about 30 miles away, where religious leaders went to work praying and leaving offerings. As days and weeks passed, the dancers overcame their choreomania and returned to their normal lives—traumatized and tired, but otherwise fine.

The dancing plague of 1518 wasn’t the only such incident of its kind. Numerous other outbreaks of uncontrollable dancing occurred in western Europe between the late 1300s and mid-1500s—and Waller thinks it’s no coincidence that many were clustered along the Rhine River and its tributaries. 

“Rivers are very good for, obviously, transporting trade goods, but they’re also very good for spreading ideas,” he says. “From the headwaters in Switzerland all the way down to where the Rhine flows into the North Sea, you’ve got this belief in a saint who curses with a dance.”

Theories behind the dancing

Now that we have the benefit of hindsight, what might explain the dancing plague of 1518 and others like it? One theory is that the dancers were sickened by ergot, a fungus that can contaminate grain. Another holds venomous spiders bit the afflicted. Demonic possession, epilepsy, typhus, and encephalitis—brain inflammation caused by an infection or autoimmune response—have also been put forward as possible explanations.

But after considering all the evidence, Waller thinks there’s only one plausible theory that truly makes sense. He suspects the dancers of Strasbourg were all victims of mass hysteria, also known as mass psychogenic illness, brought on by intense psychological distress. 

The years leading up to 1518 were rough, particularly for the lower classes, with failed crops, bad weather, economic issues, social unrest, religious tensions, and illnesses like smallpox, leprosy, and syphilis taking a toll on peoples’ psyches. They were hungry, anxious, sad, scared, and worried that God had abandoned them. 

Waller suspects the people living in Strasbourg simply reached their breaking point, then entered into a trance-like state that rendered them largely insensitive to their extreme fatigue and sore feet. They danced, Waller argues, rather than weeping, fighting, praying, or engaging in some other behavior because of their belief in St. Vitus and his dancing curse.

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Modern takeaways 

Given the period-specific cultural and religious underpinnings, could something like the dancing plague of 1518 happen today? 

Waller shares several modern examples of mass psychogenic illness that, although they don’t involve dancing, he finds to be similar in nature. More than 300 students in Blackburn, England, suffered from a mysterious fainting fit in 1956, for example, and hundreds of people succumbed to alternating fits of laughing and sobbing in East Africa in 1962. In 2007, students at a Catholic boarding school near Mexico City came down with a mysterious sickness that made walking difficult. A year later, 20 female students in Tanzania suffered a mass fainting episode during their final-year national examinations.

And although the dancing plague of 1518 took place more than 500 years ago, Waller says we can still learn plenty from it. For him, the most important takeaway is “the way in which our expression of severe distress can be culturally conditioned and channeled.” 

When Waller initially started researching the dancing plague of 1518, it was such a “wild phenomenon” that his inclination was to think “as strange as the past can be, this was simply too strange to have actually happened,” he says. But as he dug deeper—and, more importantly, began to understand the context within which it arose—it started to make more and more sense. 

In other words, he says, it reminds us that psychological distress is not expressed in a vacuum. The culture, beliefs, and circumstances around us can shape how our inner turmoil manifests—and, in some cases, how it spreads from one person to another. 

In That Time When, Popular Science tells the weirdest, most surprising, and little-known stories that shaped science, engineering, and innovation.

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In 2006, the Carabinieri, Italy’s national military police, raised the alarm about illegal digging in a forest of oaks and chestnuts near Vetralla, in the province of Viterbo, north of Rome. The Soprintendenza, the state body in charge of archaeology in the region, sent a team to the site for an emergency excavation in May […]

En 2006, los carabineros dieron la voz de alarma por unas excavaciones clandestinas en un bosque de robles y castaños del término de Vetralla, en la provincia de Viterbo, al norte de Roma. La Soprintendenza arqueológica de la Etruria meridional intervino con una excavación de urgencia entre mayo y junio y se topó con algo […]

If matter and antimatter had come out of the Big Bang in equal amounts, there would be no stars today. Every particle has an antimatter twin with the opposite electric charge, and when the two meet, both vanish in a burst of energy. A perfect balance would have left a universe of pure light, with […]

Si tras el Big Bang la materia y la antimateria se hubieran repartido a partes iguales, hoy no habría ni una sola estrella. Cada partícula de materia tiene una gemela de carga opuesta hecha de antimateria, y cuando ambas se encuentran se destruyen y se convierten en energía. Un reparto perfecto habría dejado un cosmos […]

Habían cruzado media Persia, atravesado montañas nevadas y peleado con pueblos que les tiraban piedras desde los riscos, y lo que estuvo a punto de acabar con ellos a pocos días del mar fue un panal. Ni una emboscada ni un ejército enemigo. Un puñado de colmenas, unos soldados hambrientos y una planta de flores […]

They had crossed most of Persia, climbed snowbound mountains and fought tribes that hurled stones at them from the cliffs. What left them most exposed, only a few days from the sea, was a honeycomb. There was no ambush and no enemy army, just a handful of beehives, some hungry soldiers and a flowering plant […]

Tattoos are pretty permanent decisions, and laser removal is often described as more painful than actually getting them in the first place. But what about a design that can only be seen when you want to see it? Engineers at the University of Colorado Boulder are working on a new type of tattoo ink to answer that question. Their dye is specifically concocted to physically alter depending on exposure to visible or ultraviolet (UV) light.

The team described their invention in a study published earlier this month in the journal Matter & Light, and they didn’t only demonstrate the capabilities in the lab on silicone and pig skin. One of its creators, Carson Bruns, has already tattooed himself with the ink.

“[It’s] almost a tradition,” the study co-author recently told Nature.

Bruns, a nanoscientist at UC Boulder, previously developed a now-commercialized tattoo product called “Magic Ink” that turns magenta depending on its exposure to UV light. To highlight its efficacy, Bruns gave himself “solar freckles” as a method to track his exposure to sunlight. In similar fashion, he recently completed a similar session on his leg using the disappearing ink.

The formula currently comes in three colors—yellow, blue, and magenta—and essentially relies on the same principles behind transition lenses and some textiles. Each dye is composed of tiny spheres of acrylic glass. These beads contain photochromes, which are chemical compounds engineered to absorb specific light wavelength photons. In this case, the photochomic dye’s spheres begin in their original color, but then flatten into transparency after absorbing corresponding light photons exposed to UV rays. The dye remains this way until it absorbs visible light photons, which destroys the chemical bond and allows the spheres to return to their original shape.

Aside from the lab tests, Bruns tattooed his own leg over about 12 months using various dye combinations, all of which responded as intended to UV and visible light exposure. The ink also remained effective for over two years—but the team’s intention is go beyond a nifty parlor trick. Future ink iterations may be particularly useful in medical procedures, such as temporary markings to help maintain accuracy during direct radiotherapy sessions. For now, however, the photochromic tattoo dyes remain for laboratory (and Bruns’) use only until further safety assessments are completed.

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Not far from the Black Sea, a child’s grave uncovered in present-day Bulgaria has provided archaeologists a somber look at Roman funerary practices. Flagged in the city of Stara Zagora during a site survey for a new apartment complex and parking garage project, the burial contained stunningly preserved gold earrings as well as a single, small coin known as an antoninianus. But while the currency’s age is traceable to within a year of its minting, the bronze piece may also represent a grieving family’s hopes for their child’s safe passage into the afterlife.

The Roman empire at its height included over 1.9 million square miles of territory, including much of central Europe and central Asia. Rome annexed the region of Thrace in 46 CE, and eventually renamed the city of Stara Zagora as Ulpia Augusta Traiana in honor of Emperor Trajan (98 to 117 CE). Augusta Traiana quickly grew into one of Thrace’s most prominent urban hubs, becoming so prosperous that Rome ultimately granted permission to build its own coin mint during the second and third centuries CE.

Over 1,750 years later, Augusta Traiana’s remnants exist underneath a city once again known as Stara Zagora. Ruins of the Roman empire are regularly unearthed through the town, including the recent discovery of a large cemetery used for nearly three centuries outside Augusta Traiana’s original walls. Among the 135 graves, researchers identified a child buried with a pair of gold earrings and one of Thrace’s bronze coins. Although details about the young individual’s death and identity remain unclear, the coin clearly dates to either 274 or 275 CE. Archaeologists assume the child likely died either around that time period, or soon after.

While researchers may never learn the precise circumstances of the burial, ancient Greek and Roman funerary beliefs suggest the coin served a specific purpose. It’s possible the child’s family intentionally placed the currency with the deceased as payment to Charon, the ferryman who brought souls to the afterlife. Knowing this, it may be that grieving relatives hoped to impart one final gift to their loved one.

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Japan launches a ground-breaking mission to the Mars moon Phobos today, and you can watch live.

The JAXA (Japan Aerospace Exploration Agency) MMX (Martian Moons eXploration) mission aims to collect samples from Phobos, the larger of Mars’ two moons, and deliver it back to Earth for analysis. If successful, the samples could help solve long-standing mysteries about Mars’ moons, including their origin.

In 1877, US astronomer Asaph Hall discovered Phobos and its smaller sibling, Deimos. The moons have arguably the most bad-ass names in our solar system: Phobos comes from the ancient Greek word φόβος (phobos), meaning “fear,” and Deimos originates with the ancient Greek word Δεῖμος, which translates to “dread.”

Despite increased attention on Mars in recent decades, astronomers don’t know exactly how the celestial bodies formed. Theories include asteroids or debris leftovers from way back when the solar system formed about 4.5 billion years ago.

“The samples from MMX will bring forth paradigm-shifting science on the Mars system for generations to come, especially as NASA prepares to send the first humans to Mars,” said Nicky Fox, associate administrator and Science Mission Directorate at NASA, said in a statement. While a JAXA mission, NASA worked with the agency to provide instruments and technologies to assist.

The MMX spacecraft launches on top of an H3 rocket at Japan’s Tanegashima Space Center today at 3:41 p.m. EDT (4:41 a.m. Japan Standard Time on October 20). You can watch it live on JAXA’s YouTube page. The mission will get to Phobos in August 2027 and spend at least 16 months surveying the surface before collecting samples. The samples will not return to Earth until at least 2031.

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Neanderthals left plenty of traces in the western Pyrenees, the mountain range that separates Spain from France. Stone tools, butchered animal bones, the leftovers of their camps. What nobody had ever found in Navarre, the region of northern Spain whose capital is Pamplona, was a single bone of the people themselves. On Monday that changed, […]

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Snakes will bite, rattle their tails, and even spit venom to escape danger. But of all the world’s species, southeast Asia’s dwarf reed snake (Pseudorabdion longiceps) relies on an especially fascinating escape method. When threatened, the diminutive serpent rolls away like a speeding wheel.

An adult dwarf reed snake typically measures less than 12 inches long, but its unique locomotive maneuvers allow it to retreat as fast one foot per second—about four times faster than it travels by simply slithering on the ground. It’s not a flailing getaway, either. The snake also easily rolls along a straight path while somehow keeping its head both stable and facing forward.

Now, researchers finally have a better understanding of how the dwarf reed snake achieves such dizzying acrobatics. In a study published today in the journal Current Biology, a team at Japan’s Toho University detailed the specific physiology that enables its locomotion after filming the snakes with high-speed cameras. Essentially, the snake doesn’t rotate its entire body in a singular, forward motion—it whips one side of its body forward towards the ground while an arched portion swings down by its head in what the study’s authors call a “stroke.” The snake then alternates between its left and right side coming into contact with the ground for each successive stroke. Essentially, it’s like twirling a rope in a lateral circle while holding one end in your hand—except that end is the snake’s head.

The cumulative efforts bypass the traditional idea of a wheel requiring something like a central axle. Instead, this ingenious, highly controlled movement allows the animal to keep its head and sensory organs upright and facing ahead while traveling at such high speed. This is compounded by the dwarf reed snake directing regions of its body to engage in large, alternating rotations while stabilizing its head.

By gaining better insight into these biological mechanisms, researchers also highlight the difficulty in trying to predict an animal’s capabilities based solely on its physiology. A snake may have primarily evolved to slither—but that doesn’t mean it can’t get creative when necessary.

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On a patch of bare rock in western Malta, roughly 80 by 100 metres (260 by 330 feet), dozens of parallel grooves cross, overlap and merge into one another. The spot, Misraħ Għar il-Kbir, is popularly known as Clapham Junction, after the busy railway junction in London. It is far from the only place like […]

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October is officially Bat Appreciation Month. In the spirit of the season and conservation, a team of biologists in California recently spent time finding bats at Muir Woods National Monument and Samuel P. Taylor State Park. And while Halloween is fast approaching, the activity had nothing to do with spooky festivities and everything to do with tracking hoary (Lasiurus cinereus) and western red bats (Lasiurus blossevillii). 

The goal of their survey was to put GPS trackers on bats from the two migratory species. Hoary bats have grey-white fur and are the most widespread bat species in North, Central, and South America. Western red bats, also known as southern red bats, sport a reddish fur and are found in parts of South America. In redwood forests, bats like nesting within holes inside large trees. 

“When they migrate, those little guys can cover a LOT of ground!” the Golden Gate National Recreation Area writes, referencing both species. “By learning about these migratory patterns, we can better understand entire ecosystems like Muir Woods.”

Bats are important members of such ecosystems. They are pollinators, they spread seeds, and they help manage insect populations. To catch these helpful agents, scientists set up a sheer, delicate net called a “mist net” over a creek at dusk. All bats are nocturnal, and when they went searching for their next meal—bugs—they flew into the net. 

It was a bit of a trick for the winged mammals, but a treat for the human team. “Expert bat wranglers” carefully took them out of the nets, noted their weight and size, presumably attached the GPS tracker, and then returned them to the wild. 

The Golden Gate National Recreation Area’s shared pictures of tiny, disgruntled looking bats carefully pinched between gloved fingers. In one image, an expert holds a bat wing up to the light of a colleague’s headlamp. In fact, illuminated wing membrane patterns literally shed light on the bat’s age and developmental stage.

While this survey focused on two bat species, researchers at the Muir Woods National Monument have previously spotted 10 different species.

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Hace unos 2.200 años, alguien apretó con el dedo un trozo de arcilla húmeda para pegar la solapa de una coraza. Esa presión dejó una huella que el horno selló y que ha llegado intacta hasta hoy. Ahora, un equipo del Museo del Sitio del Mausoleo del Emperador Qin Shi Huang y de la Universidad […]

About 2,200 years ago, someone pressed a finger into a lump of damp clay to stick down the flap of a suit of armour. The kiln sealed that print, and it has survived intact ever since. Now a team from the museum at the mausoleum of Qin Shi Huang and from Shandong University has used […]

In November 1983, the Soviet Union came to believe that NATO might be preparing a nuclear attack. The trigger was a war game. The alliance’s annual exercise, Able Archer 83, ran from 7 to 11 November and rehearsed what would happen if a conflict in Europe escalated until nuclear weapons were released. It even simulated […]

En noviembre de 1983 el mundo estuvo al borde de una guerra nuclear. La OTAN estaba llevando a cabo un ejercicio de simulación bélica, bautizado con el nombre de Able Archer 83 y que incluía el uso teórico de armas atómicas tras una escalada de tensión internacional, cuando el programa soviético de detección de ataques […]