5. The Shape Of Stonehenge

For a long time, historians have been divided on whether the stones at Stonehenge had originally formed a full circle. With no stones found in the southwest area, some researchers believed the structure had never been completed.

But a short hosepipe accidentally solved the mystery without excavation or expensive equipment. Tens of thousands of people had earlier overlooked the answer.

When a custodian couldn't water the grass in the entire Stonehenge area (as was usually done) due to the short hose, the grass failed to grow in the unwatered area, revealing depressions in the ground. If some of those parched areas had held stones, the circle would have been complete. Other brown patches matched areas of known archaeological excavations, confirming that the parched areas represented ground that had been intentionally disturbed.

"A lot of people assume we've excavated the entire site and everything we're ever going to know about the monument is known,” said historian Susan Greaney of English Heritage. “But actually, there's quite a lot we still don't know and there's quite a lot that can be discovered just through non-excavation methods.”

That still leaves the mystery of what happened to the missing stones. Were they used to build houses or roads in the area? No one knows, but English Heritage may purposely avoid watering some areas of Stonehenge during the next dry spell to see if the answers to other puzzles emerge.

4. The Disappearance Of The Nazca Civilization

For years, historians were baffled by the mysterious disappearance of the Nazca people of Peru around A.D. 500. This was the civilization responsible for the Nazca lines, huge geoglyphs carved into the ground in that region. There have been many theories to explain the lines, but most historians agree that the Nazca probably used them as sacred pathways when practicing their rituals.

In recent years, scientists have determined that the Nazca civilization caused its own destruction. By clearing so many huarango trees in their valleys for farming, they did irreparable damage to their environment. These nitrogen-fixing trees increased moisture and soil fertility. Without enough of them, the climate became too arid to grow food.

"The huarango . . . was an important source of food, forage, timber, and fuel for the local people," said archaeologist David Beresford-Jones. The species was responsible for "enhancing soil fertility and moisture, ameliorating desert extremes in the microclimate beneath its canopy and underpinning the floodplain with one of the deepest root systems of any tree known. In time, gradual woodland clearance crossed an ecological threshold—sharply defined in such desert environments—exposing the landscape to the region's extraordinary desert winds and the effects of El Nino floods."

Scientists believe that a major El Nino event occurred around the same time as the deforestation, triggering devastating floods due to the lack of trees. After that, the Nazca would have been unable to grow enough food for their people in that area.

3. A War Bracelet Comes Home

While serving in the Army during World War II, Warren McCauley lost or left his silver identification bracelet ("dog tag") in Castel D'Aiano, Italy in 1945. According to an Army news release that year, war hero McCauley received the Bronze Star when he "fearlessly advanced under a hail of small-arms fire to restore communications" after the German enemy cut wire lines.

While in Castel D'Aiano, McCauley stopped at the de Maria home, which the Italian family had opened to American soldiers for food and medical care. When McCauley left, his bracelet stayed behind, although no one knows if he lost it, forgot it, or left it on purpose as a kind of payment or tribute to the de Maria family. Nevertheless, Bruna de Maria, then eight years old and living there in poverty, found the bracelet and kept it as an unexpected treasure. She always lovingly cared for the bracelet but never tried to find its owner.

Decades later, her grown son, Stefano Sedda, persuaded his mother to return her treasure to its original owner. "This bracelet made history," Sedda explained. "It belonged to an American soldier who came here to fight, to defend our country—that's why I thought of giving it back."

Through a friend, Sedda contacted an American lawyer, who worked with a journalist and the Army to trace the bracelet's ID number to McCauley. Though McCauley had died 30 years earlier, they found his 85-year-old widow, Twila McCauley, living in Buena Vista, California. Warren McCauley had shared some wartime stories with his family—like the time he fell into a river and a donkey walked over him—but he'd never told them about the bracelet.

Along with the rest of her family, Mrs. McCauley was touched and grateful to have this special connection to her late husband brought home almost 70 years after it went missing.

2. The Cambyses Cover-Up

As we've discussed earlier, the lost army of Persian king Cambyses II has been a great historical mystery. Around 524 B.C., the king ordered 50,000 men into the Egyptian desert around the ancient city of Thebes (now Luxor). When the men disappeared, the official story from ancient historians said the army had been wiped out by a sandstorm.

However, modern Egyptologist Olaf Kaper was skeptical. "Since the 19th century, people have been looking for this army: amateurs, as well as professional archaeologists," Kaper said. "Some expect to find somewhere under the ground an entire army, fully equipped. However, experience has long shown that you cannot die from a sandstorm, let alone have an entire army disappear."

By piecing together information from excavations, historical records, and especially the writings of an Egyptian rebel leader (which Kaper had translated from ancient temple blocks), Kaper believes the Persian army was on its way to Dachla Oasis, where the rebel leader Petubastis III and his troops had been located. But the Persian army was ambushed by the rebel leader and suffered a crushing defeat. From his victory, Petubastis went on to reconquer much of Egypt and crown himself Pharaoh in the capital of Memphis.

According to Kaper, the Persian king Darius I put an end to this Egyptian rebellion in a bloody battle two years after Cambyses was defeated. To restore Persia's dignity, Darius covered up his predecessor's embarrassing downfall with the sandstorm story.

1. What Caused The Hindenburg Explosion

The promise of the Hindenburg, a hydrogen-filled airship that could cross the Atlantic in half the time of a ship at sea, exploded along with the craft itself as it prepared to land in Lakehurst, New Jersey in May 1937. Of the 100 people on board that day, 35 died.

Scientists have debated the reason for the explosion for decades. They knew that a spark ignited leaking hydrogen, but they differed on the reason for the spark and the leaking gas. Theories included lightning, explosive properties in paint, and a bomb.

However, in 2013, a team of experts ruled out the other theories and determined that the Hindenburg had become charged with static electricity from a thunderstorm. Either a faulty gas valve or broken wire caused hydrogen to leak into the ventilation shafts. A spark of static electricity ignited the hydrogen, which started the fire in the tail section and led to the explosion.

"I think the most likely mechanism for providing the spark is electrostatic," said British aeronautical engineer Jem Stansfield. "That starts at the top, then the flames from our experiments [blowing up or setting fire to scale models of the airship] would've probably tracked down to the center. With an explosive mixture of gas, that gave the whoomph when it got to the bottom."

注：本文转载自前十网，译者：Freya然