Ireland’s Countess of Moira, an avid antiquarian, launched these speculations in 1783 by proposing that the bodies could belong to victims of Druid ceremonies. Others have used writings of the Roman historian Tacitus from the first century A.D. to support the theory that they were executed deserters. Less convincingly, researchers in Nazi Germany searched for evidence that the bog bodies were specimens of a proto-Germanic people from which the so-called “Nordic” race descended. Despite the range of hypotheses proposed, today’s archaeologists generally agree that most of the bog bodies seem to be evidence of the Iron Age ritual of human sacrifice. First proposed in the 1950s, this theory goes that the victims could have been offerings to pacify Nordic gods like Odin or Nerthus after a bad harvest or other misfortune. However, a team of forensic investigators in Denmark examined that country’s bog bodies in recent years and determined that some damage previously believed to be evidence of torture or other violence was in fact inflicted centuries after death. The only conclusion that seems certain is that despite centuries of study, the mystery of the bog bodies endures.

From there, poker spread up the Mississippi River and throughout the country, thanks in part to its popularity among crews of riverboats transporting goods via that great waterway. Soldiers in both the North and South played poker during the Civil War, and it became a staple of Wild West saloons in frontier settlements in the 1870s and 1880s. In 1871 the game was introduced to Europe after Queen Victoria heard the U.S. minister to Great Britain explaining the game to members of her court and asked him for the rules. More general acceptance of poker in Europe occurred several decades later, largely thanks to the influence of American soldiers during World War I. Over time, different games have dominated among poker players, including five-card draw, seven-card stud and—most recently—Texas Hold’em, which began its rise to dominance in the 1970s when it became the featured game in the World Series of Poker, the game’s leading annual competition.

One enduring hypothesis for Stonehenge’s purpose comes from the initial observation, first made by 18th-century scholars, that the monument’s entrance faces the rising sun on the day of the summer solstice. For many, this orientation suggests that ancient astronomers may have used Stonehenge as a kind of solar calendar to track the movement of the sun and moon and mark the changing seasons. New excavations in recent years, however, have unearthed a different theory based on hundreds of human bones found at the site, dating across 1,000 years and showing signs of cremation before burial. The presence of these remains suggests that Stonehenge could have served as an ancient burial ground as well as a ceremonial complex and temple of the dead. In 2010 archaeologists discovered a second stone circle located just over a mile away from the more famous landmark. Dubbed “Bluestonehenge” for the 25 Welsh bluestones that originally made up the site, this secondary monument provides more evidence that Stonehenge could have been part of a huge memorial complex where high-ranking individuals took part in elaborate rituals and ceremonies honoring the dead. Yet as no written records exist, this theory—like all those about Stonehenge’s purpose—can only remain a matter of speculation.

As it turns out, the real history of baseball is a little more complicated than the Doubleday legend. References to games resembling baseball in the United States date back to the 18th century. Its most direct ancestors appear to be two English games: rounders (a children’s game brought to New England by the earliest colonists) and cricket. By the time of the American Revolution, variations of such games were being played on schoolyards and college campuses across the country. They became even more popular in newly industrialized cities where men sought work in the mid-19th century. In September 1845, a group of New York City men founded the New York Knickerbocker Baseball Club. One of them—volunteer firefighter and bank clerk Alexander Joy Cartwright—would codify a new set of rules that would form the basis for modern baseball, calling for a diamond-shaped infield, foul lines and the three-strike rule. He also abolished the dangerous practice of tagging runners by throwing balls at them.

Cartwright’s changes made the burgeoning pastime faster-paced and more challenging while clearly differentiating it from older games like cricket. In 1846, the Knickerbockers played the first official game of baseball against a team of cricket players, beginning a new, uniquely American tradition.

The popular image of the strapping Viking in a horned helmet dates back to the 1800s, when Scandinavian artists like Sweden’s Gustav Malmström included the headgear in their portrayals of the raiders. When Wagner staged his “Der Ring des Nibelungen” opera cycle in the 1870s, costume designer Carl Emil Doepler created horned helmets for the Viking characters, and an enduring stereotype was born.

Malmström, Doepler and others may have been inspired by 19th-century discoveries of ancient horned helmets that later turned out to predate the Vikings. They may also have taken a cue from ancient Greek and Roman chroniclers, who described northern Europeans wearing helmets adorned with all manner of ornaments, including horns, wings and antlers. But not only did this headgear fall out of fashion at least a century before the Vikings appeared, it was likely only donned for ceremonial purposes by Norse and Germanic priests. After all, horns’ practicality in actual combat is dubious at best. Sure, they could help intimidate enemies and maybe even poke out a few eyes, but they would have been even more likely to get entangled in a tree branch or embedded in a shield.

“World War II,” on the other hand, first appeared in print all the way back in February 1919, when a Manchester Guardian article used the term much in the way people today predict a hypothetical “World War III.” But it was Franklin D. Roosevelt who in 1941 would publicly label the conflict the “Second World War,” and his fellow Americans quickly followed suit. (In Britain, it remained simply “the War” until the late 1940s.) While Roosevelt may have helped popularize the name, it seems he wasn’t entirely satisfied with it. In 1942 he asked the public to propose alternate appellations, and over the next few weeks the War Department received 15,000 submissions ranging from “the War for Civilization” to “the War Against Enslavement.” Neither these nor Roosevelt’s own choice—“the Survival War”—had staying power. “World War II” and “Second World War” it was—and, as a result, “I” or “First” was appended to the clash that preceded it.

Most experts believe Khan was buried somewhere near his birthplace in Khentii Aimag, northeastern Mongolia, and that his descendants may be buried there along with him—but they don’t have much more to go on than that. Researchers weren’t even allowed in the area until after the Soviet occupation of Mongolia ended in the 1990s. And in the decades since, various groups have been pressured to give up their searches due to protests from the Mongolian government and public that excavation would disturb the rest of their national hero.

Such opposition has not halted the hunt. In 2004 Japanese-Mongolian researchers discovered the remains of what they think is Khan’s palace complex on the grassy steppe of Khentii Province, 150 miles east of the Mongolian capital, Ulan Bator; they believe his tomb may be somewhere nearby. And since 2008, the Valley of the Khans Project has been using cutting-edge technology to search for Khan’s final resting place. The project has enlisted thousands of “citizen scientists” to comb through high-resolution satellite images of the region looking for possible clues, giving amateurs with a home computer and an Internet connection a rare chance to help solve one of history’s most enduring riddles.

Debate has raged ever since over the extent of Jackson’s participation in the scheme. He claimed his teammates gave his name to the gamblers even though he hadn’t agreed to participate, and the other players admitted that Jackson never attended meetings about the fix. Though Jackson signed a confession in 1920 stating that he was paid $5,000 (out of the $20,000 he was promised), he later asserted that a team lawyer manipulated him into signing a document he didn’t fully understand. (Jackson never learned to read or write.) He also said he tried to return the money and talk to White Sox owner Charles Comiskey about the plan both before and after the series, but was rebuffed.

And finally, there’s the matter of Jackson’s play on the field. During the 1919 championship, the slugger made no errors and racked up 12 hits, a World Series record that stood until 1964. His batting average for the series (.375) was the highest on either team. If Jackson did try to throw the championship, his supporters argue, he did a pretty poor job. In any event, after the 1921 ban Jackson played “outlaw” ball under an assumed name before retiring to his hometown of Greenville, South Carolina, where he eventually owned a liquor store. He made various efforts to be reinstated, all of which were denied, before his death in 1951.

The brutality of the St. Valentine’s Day Massacre shocked the American public—most of which assumed Capone was behind the killings—and shifted federal authorities into high gear in their campaign against organized crime, and especially against the man they called “Public Enemy Number One.” Due to lack of hard evidence, however, no one was ever brought to trial for the murders, and some have continued to cast doubt on whether Capone—who was put away for federal income tax evasion in 1931—was actually responsible. In his 2010 book “Get Capone,” Jonathan Eig builds the case that another notorious Chicago criminal, William White (known as “Three-Fingered Jack”), might have carried out the massacre to avenge the killing of his cousin by members of the Moran gang. Other Capone experts quickly moved to debunk this theory, however, pointing to the fact that White was imprisoned at the time and that the cousin’s murder was actually linked to another gang. Though the truth of what happened that Valentine’s Day might never be fully known, the massacre has rightfully gone down in history as the bloodiest example of the gangland violence that tore America’s cities apart during the Prohibition era.

Because the human body is composed mostly of water and its only highly flammable properties are fat tissue and methane gas, the possibility of SHC being an actual phenomenon seems remote. Many scientists dismiss the theory, arguing that an undetected flame source such as a match or cigarette is the real culprit in suspected cases. Typically, deceased victims are found close to a fire source, and evidence suggests that many of them accidentally set themselves on fire while smoking or trying to light a flame.

On the other hand, believers point to the fact that the human body has to reach a temperature of roughly 3,000 degrees in order to be reduced to ashes. Unless SHC were a genuine factor, it seems impossible that furniture would not burn as well. Proposed causes of the supposed phenomenon include bacteria, static electricity, obesity, stress and—most consistently—excessive consumption of alcohol, but none have been substantiated by science so far. One recent hypothesis comes from British biologist Brian J. Ford, who in August 2012 described his experiments with combustion in the magazine New Scientist. According to Ford, a buildup of acetone in the body (which can result from alcoholism, diabetes or a specific kind of diet) can lead to spontaneous combustion.

The Alder Creek excavations, conducted in 2003 and 2004, turned up more than 16,000 bone fragments in all, including the remains of rodents, rabbits, deer, horses, oxen and cattle. They also found canine bones, supporting accounts by survivors that they ate their pet dogs. It’s clear that Donner Party members went to great lengths to avoid eating their own dead: The stranded migrants consumed a glue-like substance made from boiled animal hides, along with charred bones, twigs, leaves and bark. But despite the lack of human bones recovered from the Alder Creek site, researchers concluded that cannibalism may have occurred there in the days between the departure of the first relief party in late February and the last survivors’ abandonment of the camp in mid-March. While cannibalism may indeed be part of the Donner Party story, the Alder Creek excavations help reveal the more complicated truth behind their harrowing struggle to survive, and the desperate efforts they made to stave off such a gruesome solution.

Such a young first lady fascinated the American public and press, who called her “Frankie” (a nickname she hated). Her hairstyle was widely copied and her face appeared on souvenir coins, while bustle skirts—a previously popular style—reportedly fell out of fashion after she stopped wearing them. In 1892, when voters reelected Cleveland to a second term after a four-year gap, Frances became the only first lady to return to the White House after leaving it. In September 1893 she gave birth to the second of their three daughters, the first child born to a sitting president. (Their oldest daughter, Ruth, supposedly inspired the Baby Ruth candy bar.) Grover Cleveland died in 1908, and in 1913 Frances became the first presidential widow to remarry. She died in 1947, after living longer after leaving the White House (51 years) than any other former first lady.

Over the years, the CIA, U.S. Air Force and aerospace company Lockheed Martin have all used Area 51 as a staging ground for test flights of experimental aircraft (a.k.a. “black aircraft”). According to documents declassified in 2007, in the 1950s and 1960s Area 51 was home to a top-secret Cold War-era program known as Oxcart, which aimed to develop a spy plane that would be undetectable in the air and could be used for information gathering missions behind the Iron Curtain. The result was the Archangel-12, or A-12, which could travel at speeds of more than 2,000 miles an hour and take clear pictures of objects on the ground from an altitude of 90,000 feet. Other well-known aircraft tested there include the A-12′s successor, the SR-71 Blackbird, as well as the F-117 Nighthawk stealth fighter. From the ground, such experimental aircraft traveling at Mach-3 speeds undoubtedly resembled some people’s idea of what alien spacecraft would look like, helping to explain why so many people reported UFO sightings in the skies above Nevada over the years. Such sightings—along with the secrecy surrounding the Groom Lake site—fueled the rumors swirling around Area 51, and helped create the air of mystery it retains today.

Successful gladiators could become major stars of the Roman world, and those who were slaves could sometimes be freed after winning a certain number of matches. Some surviving gladiators became trainers themselves after their fighting days were over. In 2007 scientists discovered an 1,800-year-old graveyard at the Roman city of Ephesus, Turkey, containing thousands of bones and tombstones identifying the remains as those of gladiators. Some of the skeletons showed evidence of healed wounds, suggesting that gladiators received medical treatment, and one seemed to belong to a retired fighter. Not surprisingly, other skeletons showed signs of violent deaths, including blows from weapons such as tridents, hammers and foot-long swords. (Hammers, though not used in the arena, were used to deliver offstage death blows to fighters who were too seriously injured to survive.) There is no question that gladiatorial combat was a dangerous business, but contrary to popular myth, it did not always end in death.