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In the ‘dancing plague’ of 1518, hundreds of people danced uncontrollably for two months.

  • Dancing mania
Dancing mania
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Author Bennett Kleinman
November 29, 2023

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The phrase “dance the night away” took on a more literal meaning back in 1518, when as many as 400 people were struck by a “dancing plague” in the city of Strasbourg in modern France. The epidemic began in July with a single woman known as Frau Troffea, who spontaneously began boogying away in the middle of the street. She danced alone and continuously for an entire week before several dozen others found themselves overcome by the urge to dance as well. By month’s end, the number had grown to several hundred. The mysterious dancing eventually waned, and Strasbourg returned to normalcy in September.

Authorities were concerned by this inexplicable rise in dance fever, though ill-informed physicians attributed the ailment to “hot blood” and suggested people simply needed to dance until they no longer felt the urge. As the weeks went on, several dancers collapsed from exhaustion, and some suffered fatal heart attacks. Locals sought answers, and some feared they had been cursed by St. Vitus, the patron saint of dance. Many modern historians posit that stress, coupled with the rise of new and untreated diseases such as syphilis, likely induced this mass hysteria. There had been numerous reported outbreaks of “dancing plagues” around the Holy Roman Empire in the preceding 500 years, including a significant one in 1374. Another theory points to a fungus known as ergot, sometimes found on bread. The fungus causes convulsions if consumed, and may have been responsible for the uncontrollable dancing as well as other instances of mass panic.

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A Tanzanian boarding school suffered a laughter epidemic in 1962.

Laughter really can be contagious, as attendees of a girls’ boarding school in Tanganyika (now Tanzania) discovered in 1962. In January of that year, three students at a school in the town of Kashasha began laughing hysterically out of nowhere. The epidemic soon spread to other students, as individuals suffered laughing fits that lasted anywhere from a few hours to 16 days. With doctors unable to explain the phenomenon and students unable to focus, the school temporarily closed in March, though the issue only grew from there. The girls returned home and “infected” those communities, and entire towns were suddenly overcome with insatiable laughter. Fourteen schools closed throughout the country, with each wave of laughter lasting for around a month. In the end, there were thankfully no fatalities, though more than 1,000 people were affected by this mysterious event.

Before fingerprinting, police used ear length to identify criminals.

  • Officer measuring a prisoner’s ear
Officer measuring a prisoner's ear
Credit: © Science History Images/Alamy
Author Michael Nordine
May 20, 2026

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Even if you’ve never been hauled downtown in a paddy wagon, there’s a chance you’ve had your fingerprints taken. They’ve been used to establish people’s identities for thousands of years, but it wasn’t until the early 20th century that police used them to track criminals. 

Before that, the Bertillon system was the standard identification method in much of Europe and the U.S. It measured more than a dozen different body parts — including the ears, nose, arms, head circumference, sitting height, and standing height — to identify suspects and criminals. Eye color, scars, and other distinguishing features were noted on a standardized card that also included a mug shot.

The system was named for its creator, French anthropologist Alphonse Bertillon, who developed it in 1879. By 1898, 10 American cities including New York, Philadelphia, and Boston had begun using the system and coordinating with one another. But its flaws soon came into focus during the Will West case. Two men, named Will West and William West, who looked nearly identical and whose Bertillon measurements were likewise indistinguishable, ended up in the same prison, and it wasn’t until their fingerprints were compared that Will was able to prove his (relative) innocence. The case marked a turning point in police methodology, with fingerprinting emerging as the standard form of identification.

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Koala fingerprints are nearly indistinguishable from those of humans.

With their penchant for low-nutrition eucalyptus and high rates of chlamydia, koalas are, shall we say, special creatures — not always in a good way. Perhaps the most surprising thing about the marsupials, however, is that their fingerprints are nearly indistinguishable from ours. In fact, koalas are the only non-primates that even have fingerprints. Biological anthropologist and forensic scientist Maciej Henneberg has suggested the possibility that law enforcement might even have trouble telling human and koala fingerprints apart. “Although it is extremely unlikely that koala prints would be found at the scene of a crime,” he told The Independent in 1996, “police should at least be aware of the possibility.” In addition to providing better grip strength for climbing, fingerprints provide greater sensitivity when inspecting food sources — a helpful trait for koalas, who are famously finicky when it comes to what they eat.

Archaeologists have found 3,000-year-old pots of honey that are still edible.

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Wooden honey stick
Credit: Naffisa/ Shutterstock
Author Nicole Villeneuve
November 21, 2023

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Ancient Egyptian royals were often buried with objects they believed were needed for a harmonious transition to the afterlife. Items such as jewelry and games were common inclusions in their tombs, as were everyday staples such as clothing and food. And while we might expect any ancient food to decompose past the point of recognition, archaeologists have actually uncovered 3,000-year-old pots of honey that were, remarkably, intact — and still edible.

Honey’s extraordinary shelf life is the result of several factors. Its low water content and high sugar levels create an environment that’s inhospitable to bacterial growth, and it also contains trace amounts of hydrogen peroxide, which acts as a natural microbial inhibitor. While other foods with similar sugar makeup tend to spoil faster, honey has its sophisticated alchemists to thank for its resilience: Bees use their rapidly flapping wings to evaporate most of the honey’s water, and an enzyme in their stomachs contributes to honey’s unique antibacterial property. Egyptians were some of the earliest known organized beekeepers, and along with sending honey into the next life with the deceased, they also offered the sweet substance to their deities.

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The bear that inspired Winnie-the-Pooh preferred condensed milk.

Winnie-the-Pooh is often seen in books or cartoons with a paw in a jar of honey. But the real-life bear that Pooh was based on preferred a different sweet snack: condensed milk and, sometimes, corn syrup. The inspiration for the Winnie-the-Pooh children’s book was a Canadian black bear cub who was adopted by a soldier named Harry Colebourn during World War I. Colebourn named the bear after his hometown of Winnipeg — “Winnie” for short — and trained the bear with rewards of condensed milk and corn syrup. He eventually donated the bear to the London Zoo, where she became a popular attraction. Local author A.A. Milne’s son, Christopher Robin Milne, often visited the zoo and became smitten with Winnie, spending time with her and doling out one of her favorite snacks: condensed milk. 

Theodore Roosevelt named the White House.

  • The White House, 1900
The White House, 1900
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Author Bennett Kleinman
May 14, 2026

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America’s first 25 presidents didn’t live in the White House — or at least, they didn’t call it that. Upon its completion in 1800, the building at 1600 Pennsylvania Avenue was known as the President’s Palace. Its name was then officially changed to the Executive Mansion in 1810 to avoid regal undertones. The building wasn’t formally named the White House until the presidency of Theodore Roosevelt. 

The nickname “White House” first emerged around 1811, as evidenced by an April 24 letter from British diplomat Francis J. Jackson to former Secretary of State Timothy Pickering. The informal moniker arose because the building’s white-gray color made it stand out from the many nearby structures predominantly made of red brick.

While this nickname remained popular, the name wasn’t formalized until 1901, roughly one month into Teddy Roosevelt’s presidency. In an October 17 letter sent by the president’s personal secretary George B. Cortelyou to Secretary of State John Hay, staff were directed to “change the headings, or date lines, of all official papers and documents requiring his signature, from ‘Executive Mansion’ to ‘White House.’” 

According to Roosevelt’s Presidential Library, the name change was part of an ongoing effort to modernize the presidency and reaffirm the building as a symbol of the people it serves, rather than a private mansion.

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Three official presidential residences existed before the White House.

When George Washington assumed the presidency in 1789, the White House was still 11 years from completion and the national capital was in New York City. So from the start of Washington’s term on April 30 until February 23, 1790, his official residence was the Samuel Osgood House (named for the politician who owned it) in Lower Manhattan. Washington later moved into a nearby residence owned by land speculator Alexander Macomb, which served as the second official presidential home until August 30, 1790. In late 1790, the nation’s capital shifted to Philadelphia, and so too did its leader, who moved into a home owned by merchant Robert Morris. Washington remained there until leaving office in 1797. His successor John Adams lived in the Morris house for the first three years of his presidential term, before moving to the White House in Washington, D.C., on November 1, 1800.

Twelve percent of the U.S. population served in World War II.

  • U.S. recruitment office, 1940
U.S. recruitment office, 1940
Credit: Hulton Archive via Getty Images
Author Michael Nordine
March 13, 2025

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When Congress declared war on Japan on December 8, 1941, more Americans than ever before heard the call of duty. Some 16.1 million U.S. citizens served in the military by the time World War II ended in 1945, representing 12% of the total population of 132 million at the time. Around 39% of U.S. service members were volunteers, while the remaining 61% were draftees. It was the second-deadliest conflict in U.S. history, with the 407,316 fatalities surpassed only by the 620,000 or more who fell during the Civil War. 

The average duration of service was 33 months, with 73% of Americans serving overseas in countries such as France and Germany for an average of 16 months. An enlisted soldier earned an average of $71.33 per month, while officers made $203.50 per month — equivalent to about $1,436 and $4,107 today, respectively. 

The number of service members was even higher in Germany, where 18.1 million aided the Nazis’ effort out of a population of 69 million — a whopping 31%. No nation bore the brunt of the conflict quite like the Soviet Union, however, where 34.5 million people, including 35% of the male population, mobilized during the war.

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World War II was fought on every continent but Antarctica.

Though it was divided into two main theaters (Pacific and European), World War II was so expansive that it was fought on every continent but one: Antarctica. The North Africa campaigns lasted three years and saw battles take place in Libya, Egypt, Morocco, Algeria, and Tunisia, with the Allies emerging victorious in May 1943. The conflict also reached North America; the U.S. entered the war after the Pearl Harbor attack of December 7, 1941, which President Franklin D. Roosevelt famously declared “a date which will live in infamy.” Brazil was the only South American country to deploy troops, but naval battles such as River Plate occurred off the coast of Uruguay, and Germany attempted espionage in Latin America via Operation Bolívar. Australia was one of the first countries to declare war on Nazi Germany, and mainland Australia was first attacked by Japan on February 19, 1942.

Machu Picchu is younger than Notre-Dame Cathedral.

  • Machu Picchu
Machu Picchu
Credit: © earleliason—iStock/Getty Images
Author Bess Lovejoy
May 14, 2026

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Perched high in the Andes, Machu Picchu feels like a relic from the deep past — a lost city swallowed by clouds and time. But despite its ancient aura, it’s actually younger than one of Europe’s most famous medieval landmarks: Notre-Dame Cathedral.

Construction on Notre-Dame began in 1163, and the cathedral rose over the next two centuries into a defining example of Gothic architecture. By the time it was finished around 1345, it had already become a centerpiece of Parisian religious and civic life. 

Machu Picchu, by contrast, dates to the height of the Inca Empire in the 15th century, likely built as a royal estate for the emperor Pachacuti. For decades, historians placed its construction around 1450, but newer research using radiocarbon dating suggests the site may have been occupied as early as the 1420s (and possibly even a little earlier, as scientists continue refining the timeline). Still, Notre-Dame stood for centuries before it.
The comparison highlights two very different historical trajectories. While European builders were perfecting cathedral construction in the Late Middle Ages, the Inca were developing their own sophisticated architectural traditions in the Andes, shaping stone so precisely that structures could stand without mortar. But eventually, Machu Picchu was abandoned around the time of the Spanish conquest in the 16th century.

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Spanish chronicles don’t mention Machu Picchu.

When Spanish conquistadors swept through the Inca Empire in the 1530s, they left behind detailed written accounts of the places they encountered — but Machu Picchu is nowhere to be found in those records.

That silence has long puzzled historians. One leading theory is that the remote mountaintop site, tucked deep in the Andes above the Urubamba River, simply escaped the Spaniards’ notice. Another possibility is more intriguing: that Machu Picchu may have served as a kind of refuge during the early years of Spanish conquest, where some Incas could retreat beyond the reach of colonial forces.

There’s no definitive proof for that idea, and many scholars think the site was likely abandoned around the time the Spanish arrived, as the political and economic systems that sustained it collapsed. Still, the lack of any mention in colonial chronicles remains striking — especially for a site of such scale and sophistication.

John Wilkes Booth’s brother saved the life of Abraham Lincoln’s son.

  • President Lincoln and family
President Lincoln and family
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Author Michael Nordine
December 7, 2023

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John Wilkes Booth will forever be infamous for assassinating the man widely regarded as the greatest president in American history, but not all Lincoln-Booth relations were strained. A year or two before Honest Abe’s death, in fact, Edwin Booth — the older brother of John and a prominent actor — saved the life of Lincoln’s son Robert Todd Lincoln, who was then in his early 20s. (The precise date is unknown, but the event is believed to have taken place in either 1863 or 1864.)

The younger Lincoln found himself on a crowded train platform in Jersey City, New Jersey, and was accidentally pushed off the platform as a train departed. “In this situation the train began to move, and by the motion I was twisted off my feet, and had dropped somewhat, with feet downward, into the open space, and was personally helpless,” Robert Todd Lincoln later wrote of the event that put him in the path of the oncoming train. It was then that Booth grabbed him by the coat collar, saving him. Booth was well known enough as an actor for Lincoln to recognize his rescuer and even thank him by name. In April 1865, the day after his brother assassinated Lincoln, Edwin vowed never to return to the stage — a short-lived promise, as he gave an acclaimed performance in the title role of Hamlet the following year.

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John Wilkes Booth originally planned to kidnap Lincoln.

“All plots tend to move deathward,” wrote Don DeLillo in the 1985 novel White Noise, and so it was with Booth and Lincoln. Booth, a disgruntled actor and fierce Confederate sympathizer, originally had a less violent plan — to kidnap the president, hold him in Richmond, Virginia (the capital of the Confederacy), and exchange him for a number of Confederate prisoners. He came close to carrying out this plan on March 17, 1865, before Lincoln’s schedule changed at the last minute and he did not attend the play where the kidnapping was to take place. “My love (as things stand to-day) is for the South alone,” Booth wrote to his brother-in-law in 1864. “Nor do I deem it a dishonor in attempting to make for her a prisoner of this man to whom she owes so much misery.” The plot was forever scuttled when the Confederacy surrendered less than a month later on April 9. Just five days later, Booth executed the more extreme version of his plan.

Napoleon almost wasn’t French.

  • Portrait of Napoleon Bonaparte
Portrait of Napoleon Bonaparte
Credit: © mikroman6—Moment/Getty Images
Author Bess Lovejoy
May 14, 2026

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Napoleon Bonaparte is one of France’s most famous figures, but at birth, his identity was far less straightforward. He entered the world as Napoleone di Buonaparte on August 15, 1769, in Ajaccio, the capital of the Mediterranean island of Corsica. At the time, France had only just acquired the island from Genoa the previous year, after 500 years of Genoese control. In practical terms, Napoleon was born into a place that had only just become French — and didn’t yet fully feel it.

Corsica itself had long been shaped by Italian influence, and that cultural imprint was evident in Napoleon’s family, language, and name. French was not his first language (it was a local dialect similar to Italian), and as a young man, he was more interested in Corsican politics than in France’s future. That outsider status became even clearer when he was sent to mainland France for school. There, classmates mocked his accent and made fun of his name.

Napoleon’s transformation came later. After the French Revolution, he aligned himself with France’s new political order and began reshaping his identity along with it. He dropped the more Italian-sounding elements of his name and became “Napoleon Bonaparte,” a figure who would rise through the French army and eventually rule the country. In retrospect, it’s striking that the leader who came to embody France was born at the margins of it — culturally, linguistically, and politically.

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Napoleon and his family had to flee Corsica in 1793.

Napoleon’s path to embracing a French identity wasn’t just gradual — it was forced. In the early 1790s, amid the upheaval of the French Revolution, Corsica descended into political conflict. The island’s independence leader, Pasquale Paoli, broke with revolutionary France and sought autonomy for Corsica, with British support. The Bonaparte family sided with the French Republic, a dangerous choice. By June 1793, Paoli’s followers had branded the Bonapartes as traitors. Their home in Ajaccio was looted, and the family faced what contemporary accounts describe as mortal danger. They fled the island for mainland France. The exile proved decisive: Up until then, the young Napoleon had been closely tied to Corsica, returning often and focusing on Corsican politics. Losing that foothold pushed him to fully commit to a career in the French army.

Genghis Khan was the leader’s title, not his name.

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Genghis Khan
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Author Sarah Anne Lloyd
March 20, 2025

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The mighty conqueror Genghis Khan is one of history’s most formidable world leaders, but his legacy is far better known than his actual name. He was born to a ruling Mongol family and was given the name Temüjin, which means “of iron” or “blacksmith” in the Mongolian language. Temüjin was sent into exile with his mother and siblings when he was 9 years old, after his father was poisoned by political enemies. Despite living in poverty and even a brief enslavement, he clawed his way back to power by killing leaders of rival tribes and gathering allies. By his early 20s, he had emerged as a tribal leader with a large, loyal army.

In 1206, when Temüjin was in his late 30s to mid-40s (his birth year is the subject of debate), he gathered leaders — the ones he hadn’t killed — from all over the Mongolian Steppe to unite them as one nation, ready to conquer neighboring lands. At this assembly, called a kurultai, he was given the title of Genghis Khan. “Khan” is a Mongolian word for “leader” or “ruler,” although its use spread more widely in the following centuries. “Genghis,” also spelled “Chinggis,” is usually translated as “universal,” although it could have also meant “ocean” or “just.”

While he had risen to power as Temüjin, the leader built his empire as Genghis Khan. By his death in 1227, the Mongol Empire reached north to Siberia, south to Tibet, west to the Caspian Sea, and east to the China Sea. His children and grandchildren, including the famed ruler Kublai Khan, went on to grow the territory to around 9 million square miles, making it what is still the largest contiguous land empire in history. Genghis Khan’s immediate successor, Ögödei, used the title khagan, meaning “Great Khan.”

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The Mongol Empire had its sights on Western Europe.

The Mongol Empire was vast, and included significant parts of Eastern Europe. The Golden Horde — the western portion of the empire, led by Genghis Khan’s grandson Batu — conquered Kyiv in 1240. They laid waste to Hungary and mounted the head of Henry II, Duke of Silesia (now Poland), on a pike. Some Silesians were so terrified of the approaching army that they torched their own city and hid. Batu’s cavalry pushed its way into Bohemia in the spring of 1242, but abruptly turned back and pulled out of Hungary altogether instead of pushing further into Western Europe. There’s some debate as to why, but there are a couple of compelling theories. First, Ögödei, the Great Khan, had died in December 1241, and word may have just reached Batu that he needed to go back and help pick a successor at the kurultai. Second, the climate in the region had recently taken a really, really bad turn: The temperature was cold, the path was marshy, and food was scarce for both humans and horses, so the Mongols may have realized that moving forward wasn’t feasible.

Dreams were used for medical diagnoses in ancient times.

  • Illustration of Roman woman sleeping
Illustration of Roman woman sleeping
Credit: © Nastasic—DigitalVision Vectors/Getty Images
Author Michael Nordine
May 14, 2026

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Dreams mystified the ancient Greeks and Romans even more than they puzzle us, and both civilizations’ greatest minds attributed all manner of meanings to them: prophetic, divine, and even medical. (And you thought asking ChatGPT for medical advice was questionable.) 

Dreams were used as diagnostic tools by ancient physicians, including one of the most influential doctors in history: the Greek physician Galen, who wrote about the practice in a text called On Diagnosis in Dreams in the second century CE. He and others of his time believed that health was governed largely by the four humors — blood, phlegm, yellow bile, and black bile — and that too much or too little of any one humor resulted in illness. 

According to the theory, a person’s dreams corresponded with their ailments. “Someone dreaming a conflagration is troubled by yellow bile, but if he dreams of smoke, or mist, or deep darkness, by black bile,” Galen wrote in On Diagnosis in Dreams. “Rainstorm indicates that cold moisture abounds; snow, ice, and hail, cold phlegm.” The idea that dreams could be used in this diagnostic manner was a controversial one even then, and Galen wrote his text in defense of the practice. Humorism fell out of favor by the mid-19th century, when the development (and, in the following decades, acceptance) of the germ theory of disease changed medicine forever.

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Rome was the first city with a population of 1 million.

Rome is not currently among the 100 most populous cities in the world, but it reached a significant milestone more than 2,000 years ago: the first city with a million people, which it achieved in 133 BCE. Cities that have been the most populous in the world since then include Baghdad, Iraq; Cordova, Spain; Polonnaruwa, Sri Lanka; Ayutthaya, Thailand; and London, England. Tokyo, Japan, recently lost the title to Jakarta, Indonesia, which is home to roughly 42 million people.

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