The Forbidden City, Beijing: North-western angle

Hanging Monastery, a temple with the combination of Taoism, Buddhism, and Confucianism.

In 1900, a crew of Greek sponge divers got caught in a storm and took shelter near a tiny island called Antikythera. When the weather cleared, one of them dove down to look for sponges. He came back up shaken, saying the seafloor was covered in dead bodies and horses. They were bronze statues. He'd found a Roman-era shipwreck, about 2,000 years old, loaded with Greek treasure. The divers hauled up statues, glassware, pottery, and jewelry with almost no equipment. It was brutal work. One diver died and two were paralyzed by the bends. Among the haul was a shoebox-sized lump of corroded bronze and wood. Nobody thought much of it. It sat in the National Museum in Athens. Then in 1902, an archaeologist named Valerios Stais looked closer and noticed something inside the lump. A gear wheel. Ancient Greeks weren't supposed to have gears like that. For most of the 20th century, scholars argued about what it was. The real breakthrough came in 2005, when researchers ran it through high-powered X-ray CT scans and read thousands of tiny letters hidden inside the fragments. It was a computer. A hand-cranked mechanical one. Turn the handle and it showed the positions of the sun and moon, the phases of the moon, and the dates of eclipses years in advance. It even modeled the way the moon speeds up and slows down in its orbit using a clever pin-and-slot gear. And one dial tracked the four-year cycle of the Olympic Games. It's usually dated to the 2nd or early 1st century BC. More than 30 gears survive. Nothing with this kind of gearing shows up again in the historical record for well over a thousand years. We have no idea who built it. We don't know if it was one of a kind or if there were others that were melted down for scrap. Bronze was valuable, and almost all of it got recycled. This one survived for a simple reason. It sank. Everything we think we know about what the ancients could do is based on what happened to survive. The Antikythera mechanism is proof that some of the best stuff didn't.

October 5, 610. A rebel fleet from North Africa sails into Constantinople, and the emperor of the Roman world is dragged out of his palace in chains. The emperor was Phocas, a junior officer who had seized the throne eight years earlier in an army mutiny. He had the previous emperor, Maurice, executed, but only after forcing him to watch his five sons killed first. Phocas ruled through terror, purges, and torture, while Persia used the murder of Maurice as an excuse to invade and tear the eastern provinces apart. In Carthage, the governor of Roman Africa decided he'd had enough. He sent his son, also named Heraclius, east with a fleet, while a cousin marched overland to take Egypt and cut off the capital's grain. When the fleet reached Constantinople, Phocas's support collapsed almost overnight. Even his own son-in-law, the commander of the palace guard, switched sides. Phocas was captured and brought aboard Heraclius's ship. According to one account, Heraclius looked at him and asked, "Is this how you have ruled?" Phocas answered, "Will you rule any better?" Heraclius had him executed on the spot. His body was mutilated and paraded through the city. That same day, Heraclius was crowned emperor and married his bride. He would go on to crush Persia in one of the greatest comebacks in Roman history, only to watch the newly united Arab armies take Syria, Jerusalem, and Egypt before he died.

Map of the Greek and Latin states in southern Greece ca. 1278

Jean-Paul Laurens - The Byzantine Emperor Honorius - 1880

Caerlaverock Castle, a 13th-century castle in southern Scotland

Bodiam Castle, a 14th-century castle near Robertsbridge in East Sussex, England

Almost everything we know about ancient writing survived because it stayed dry. Deserts. Sealed caves. Baked clay. The Vindolanda tablets survived because they were soaking wet. Vindolanda was a Roman fort in northern England, just south of where Hadrian's Wall would be built. Around 100 AD, the soldiers and officers there wrote letters and lists on thin slices of wood, about the size of a postcard, in ink. When the garrison rebuilt the fort, they dumped old trash and paperwork on the floor and buried it under new layers of clay and turf. The ground was waterlogged. With no oxygen, nothing rotted. In 1973, archaeologist Robin Birley was digging there and pulled up what looked like wood shavings. Then he noticed faint ink on them. They had to use infrared photography to read most of it. What came out was the Roman army in its own words, and it's way more human than anyone expected. A cavalry officer writes to his commander that his men have run out of beer and asks him to send more. Someone sends a soldier a package with socks, sandals, and two pairs of underpants. It was cold up there. A unit strength report lists 752 men. Over 450 were away on other duties. Of the ones who were actually there, 15 were sick, 6 were wounded, and 10 had eye infections. An intelligence note sizes up the locals and calls them "Brittunculi." Basically "wretched little Britons." And the most famous one is a birthday party invitation. An officer's wife named Claudia Severa invites her friend Sulpicia Lepidina to her party. A scribe wrote most of it, but at the bottom Claudia added a few lines in her own hand, telling her friend she's looking forward to seeing her. Those few lines are thought to be the earliest known writing in Latin by a woman. They're still finding tablets at Vindolanda today. The count is well over a thousand. We usually picture Rome through emperors and battles. At Vindolanda, it's beer orders, cold feet, and a birthday party at the edge of the empire.

View of Maijishan hill caves, grottoes and stairways.

The Roman Empire under Hadrian, showing the legions deployed in its senatorial provinces

Trajan's Bridge remains at Danube’s northern bank

Tomb of Pharaoh Tutankhamun (1323 BC) — the only unlooted royal tomb ever found, with over 5,000 pristine artifacts sealed for 3,245 years

A possible representation of Trajan’s bridge, the ancient Roman superstructure

Engraving depicting Caesar Augustus' now lost painting of Cleopatra VII in encaustic, which was discovered at Emperor Hadrian's Villa (near Tivoli, Italy) in 1818. She is seen here wearing the golden radiant crown of the Ptolemaic rulers and being bitten by an asp in an act of suicide. She also wears the knot of Isis around her neck, which corresponds to Plutarch's description of her wearing the robes of the Egyptian goddess Isis

Equestrian statue of Frederick the Great in the Amber Chamber, Autochrome Lumière in 1917

An intact pyramid capstone, one of the few know in existence

Victorian depiction of a Macedonian phalanx at the Battle of the Carts

October 4, AD 23. Rebels storm Chang'an, capital of China, and hunt down the man who stole the Han throne. His name was Wang Mang. In AD 9 he pushed aside the Han dynasty and declared his own, the Xin, meaning "New." He launched some of the most radical reforms in Chinese history: seizing land to redistribute it, banning the sale of slaves, and replacing the currency over and over until nobody trusted money anymore. Then nature turned on him. The Yellow River broke its banks and changed course, flooding huge stretches of farmland. Famine spread. Peasant armies rose up across the country, including one whose fighters painted their eyebrows red so they could tell friend from foe. By the autumn of AD 23, rebels were breaking into the capital. Wang Mang, now in his late 60s, refused to run. He sat in his palace holding a ceremonial dagger, with an astrologer turning his seat to follow the stars, convinced Heaven would not let him fall. It did. As the palace burned, he fled to a tower in the middle of a lake. The rebels found him there and killed him. Soldiers fought over his body and hacked it apart. His head was kept as a trophy in the imperial treasury. It stayed there for nearly three centuries, until a fire destroyed it in AD 295. Two years after his death, a Han prince restored the dynasty. Wang Mang's "New" dynasty lasted just 14 years.