The stone boxes waited in the darkness, each one a coffin of granite large enough to hold a small room. They had been sealed for thousands of years, and when explorers finally pried them open in the nineteenth century, they found nothing inside but the bones of bulls. That was odd enough. But the boxes themselves were the real puzzle: massive sarcophagi weighing around seventy tons, cut with perfectly straight angles and smooth surfaces, carved from granite so hard that working it should have taken generations of labor.
The men who built them had no iron tools that anyone could find, no record of how they did it, and no explanation for why they made the boxes so enormous when the pharaohs themselves were buried in coffins that were tiny by comparison. The Serapeum of Saqqara was discovered by accident in 1850, when a French scientist stumbled onto a long underground hallway flanked by giant stone rooms. Inside those rooms sat the granite sarcophagi, built not for people but for the sacred Apis bulls, animals the Egyptians treated like royalty because they believed the bulls were chosen by the gods. The Egyptians thought these bulls were incarnations of the deity Ptah, with magical powers to protect the kingdom.
Scientists found roller marks on the floor and wooden winches with levers, which suggested how the workers moved the sarcophagi: they filled the burial chambers with sand, rolled the stone boxes into place, and then slowly removed the sand to lower them perfectly into position. A stone inscription found in the Serapeum said it took twenty-eight days just to move one of these boxes. Some people believe the boxes were not tombs at all. They point out that the Egyptians knew about fermentation, and they argue that if someone placed food or meat inside a perfectly sealed granite box and let fermentation happen, pressure would build up inside.
Granite contains quartz, a crystal that creates electricity when squeezed. As the pressure increased, the lid could pop open, releasing gas. Ancient drawings found in the Serapeum show stones stacked on top of the boxes, which might have made the lids even heavier and helped produce more electricity. Scientists still are not sure if the massive stone boxes were ancient energy systems, and so the mystery lives on.
The Serapeum is only one of many ancient places that raise more questions than they answer. On the other side of the world, in the Andes Mountains of Bolivia, sits Puma Punku, a stone complex so precisely built that some people refuse to believe humans made it. The site is part of the ancient city of Tiwanaku, near Lake Titicaca, a place so important in Inca tradition that they believed it was where the world was created. Historians think Puma Punku was built around 536 AD, and the first Europeans discovered it in the middle of the sixteenth century.
At its heart is a huge terrace platform filled with massive stone blocks, some as big as a school bus. The largest one weighs 131 tons, heavier than twenty elephants. Even the smaller rocks are as big as a couch. The site is built from two types of stone: red sandstone and andesite, one of the hardest rocks on Earth.
The H-shaped blocks fit together like puzzle pieces, all looking the same, as if they were mass-produced in a factory. That should have been impossible for an ancient civilization. The builders made perfectly straight lines, cut identical angles, created smooth surfaces, and drilled holes with precise grooves to hold metal clamps. It took another thousand years before other civilizations could match that level of precision.
But how did they do it? The Tiwanaku people never wrote down their methods. They had no wheels, no cranes, no modern machines, and no metal tools that archaeologists ever found. Yet somehow they moved these enormous stones miles from their original locations, up into the mountains at 12,600 feet above sea level, so high that even trees do not grow there.
Some scientists think they used llama skin ropes and ramps. Others believe the ancient builders might have had a way to soften stone to make it easier to carve before it hardened again, or that they poured liquid stone into molds like we make concrete today. Local legends say powerful deities used incredible powers to lift and shape the massive blocks. And some people believe the builders must have had help from visitors from outer space, pointing to carvings at Tiwanaku that show figures wearing helmet-like shapes.
Scientists from the University of California, Los Angeles decided to test that theory. They created a digital model of Puma Punku using precise measurements from historical records, then used a 3D printer to make a miniature version of the site at four percent of its original size. When they finished the model, they realized one of the buildings had a design that looked just like structures from two nearby sites. That, they said, was solid proof that Puma Punku was built by humans, not space travelers.
The mystery of lost civilizations extends beneath the sea as well. Off the coast of Egypt, archaeologists exploring the lost city of Thonis-Heracleion have been pulling gold and silver treasures from the water. The city sank more than a thousand years ago, and nobody even knew where it was until it was rediscovered in 2000. On a recent dive, researchers found a pile of gold and silver treasures, probably used in rituals to bless Egyptian pharaohs when they took the throne.
They also found an ancient Greek temple dedicated to Aphrodite and some very old Greek weapons. Frank Goddio, the lead archaeologist, said it was astonishing that those delicate objects had survived the disaster that brought the city down. Back in its prime, Thonis-Heracleion was one of the biggest port cities in the Mediterranean, the main entry point for ships from Greece coming into Egypt. But rising waters, earthquakes, and a catastrophic tidal wave turned the soil underneath the city into mush, and the entire city sank into the Mediterranean.
It was forgotten until Goddio’s team found it in 2000, and they have been uncovering new parts of it ever since. The search for lost cities has also moved deep into the Amazon rainforest, where for centuries people told stories of places like El Dorado, the mythical city of gold that lured Spanish explorers into the jungle, many of whom never came back. In the early 1900s, a British explorer named Percy Fawcett went searching for what he called the Lost City of Z, and he too disappeared. Now scientists have found proof that those lost cities were real.
Using lidar, a technology that bounces light beams off the ground to see through thick jungle from above, a team flew over the jungle in Bolivia in a helicopter about 650 feet up and mapped hidden ancient cities. What they found were ruins of a huge urban settlement built by the Casarabe people, who lived there from 500 to 1400 AD. The lidar maps revealed massive urban centers with pyramids, platforms, roads, canals, and causeways, all carefully laid out. Twenty-six sites were discovered, including eleven that no one even knew existed.
Two main city sites, Landívar and Cotoca, had massive moat-causeways stretching out like spokes on a wheel, linking the main cities with smaller surrounding settlements. Some of the canals connected the cities to rivers and a big lake, allowing water to flow through the area. The Casarabe culture had a thriving society in an area that faced huge challenges like yearly flooding, and they built reservoirs to store water, which suggests they were dealing with occasional droughts. Those droughts could be why the Casarabe eventually left their cities around 1400 AD.
Elsewhere in the Americas, another ancient city has puzzled researchers for a different reason. Cahokia, near St. Louis, Missouri, was a huge city with up to 20,000 people living there in the eleventh century. It is full of massive earthen mounds built by hand, and the biggest one is still there today.
Researchers have found old teeth at the site, and after studying their structure, scientists suggest that a lot of different indigenous groups lived there. About a third of them came from other areas in the middle of the continent, figured out by studying the different levels of various substances in the teeth. The way the mounds are arranged shows the city was planned out, not just a bunch of villages grouped together. The rulers lived on top of the mounds while everyone else lived in other structures.
In the middle of Cahokia was a giant mound about 100 feet tall, surrounded by a huge wooden fence. Inside the fence was the city center with a big open space called a plaza. Archaeologists think the plaza was designed to represent the four cardinal directions of the world, like the people who built it wanted to create a place in harmony with the universe. What became of the city is hard to tell.
Some think the people cut down too many trees and the land got messed up. Others believe that is not true because the soil was still in good shape after the city was gone. There is also a theory that fights with other communities caused the city to collapse. Mohenjo-Daro, in modern-day Pakistan, is another lost city surrounded by mystery.
It flourished during the Bronze Age and was extremely advanced for its time, with water systems and fancy architecture that other cities did not have. Archaeologists found the city in 1911, but it took a while for them to realize how important it was. Excavations uncovered over 700 wells, private baths, and a large communal bath. Even private homes had toilets, and waste was disposed of through a city-wide sewage system.
The people had trade connections and made beautiful objects like pottery, jewelry, and figurines that were sold all over the region. Despite its amazing culture, scientists have yet to figure out why the city was abandoned. Some think changes in the nearby river might have had something to do with it. The writings the people left behind are still a complex code even for the most skilled specialists.
In the Namib Desert, the town of Kolmanskop tells a different kind of story. It used to be a small settlement that got its name from a man named Coleman who got stuck in the local dunes and was never seen again. In 1908, a railway worker found a shiny stone and showed it to the chief railway foreman, who turned out to be a hobby mineralogist. They discovered it was a diamond, and soon Kolmanskop became the richest town in Africa and one of the richest places in the world.
It had luxurious stone houses, a school, a hospital, and even an ice factory. The hospital had the first X-ray machine in southern Africa, supposedly used to check if workers were illegally swallowing diamonds. Its popularity declined in the late 1920s when another diamond-rich location was discovered nearby. Most inhabitants fled, and in 1938 all machinery was taken south and the town was left to the desert.
The last inhabitant left between 1956 and 1960. The hot climate and low humidity preserved the structures, and tourists can now visit this desert ghost town. Machu Picchu in Peru remains one of the most famous ancient sites in the world, yet scientists are not exactly sure what it was used for. It could have supported up to 750 people, but there are not a lot of human clues left behind.
Some think it was a spiritual or ceremonial place, others believe it may have been a retreat for nobles, and there is even a theory that it was used as a prison because they found a cell-like area. The builders probably did not even use wheels for transportation, yet they somehow pushed massive granite rocks up the steep Andean mountains. Historians think hundreds of people worked together to push each rock up the peak. The stones are so close together that you cannot see any cracks between them, which makes the area safe during earthquakes because the stones move a little bit and then go back to their original spot.
The citadel is built on a fault, so the builders had to move a bunch of stone and earth to make it flat. Scientists think the real construction is actually underground because of deep foundations and a drainage system, including a hidden water system discovered using 3D scanning. The builders did not use mortar, and the blocks were so precise that you cannot fit a sheet of paper between them. One theory suggests the people used stone tools made of a harder material than the stone they were cutting.
Not every mystery involves a lost city. Beneath the surface of the Earth itself, humans have built and discovered things that still astonish. During the 1960s, humans tried digging the deepest man-made hole on Earth, deep in the Arctic Circle. What became known as the Kola Superdeep Borehole reached a depth of 40,230 feet, and it took twenty years to drill that far into the Earth’s crust.
Researchers say that is only about a third of the way through to the mantle. The crust of the Earth is only about 25 miles thick, and the thinnest part is on the ocean floor. When American scientists understood that, they started drilling holes on the seabed, a project called Project Mohole that began in 1961. Their technology for drilling deep holes on the ocean was bad, so they had to improvise, installing a system of propellers along the sides of their drill ship to keep it steady over the hole.
The main challenge was to drill as vertically as possible, or the deep hole would look more like a maze. Both projects came to an official stop in the years that followed. But humans have built some pretty deep things underground too. In 1963, a Turkish man took a swing with a sledgehammer to improve his basement and discovered a tunnel.
That tunnel entrance led to more openings that connected a multitude of halls and chambers. He had discovered Derinkuyu, a once-lost city up to eighteen stories tall and 200 feet deep, large enough to host 20,000 people, standing beneath Cappadocia in Turkey the whole time. Cappadocia hosts hundreds of subterranean dwellings, and forty of these underground cities are at least two stories high, but none of them are as huge as Derinkuyu. Some speculate the oldest part of the complex was dug about 2,000 BC by the Hittites, who built it to protect themselves from invasion.
Others think Christians built the city in the first century AD to protect people from extreme temperatures. The rocks under Cappadocia are soft, which makes tunneling easier, but for that same reason the caves are fragile, which is why most chambers have pillars supporting them. None of the floors at Derinkuyu have ever collapsed. The city was shut off from the world by huge rocks that hid its entrance, and it was ventilated by more than 15,000 shafts around 10 centimeters wide.
The upper levels were used as living and sleeping quarters, the lower levels for storage. There was a room for a wine press, stalls for domestic animals, and small religious buildings. Switzerland also built something impressive underground: the Gotthard Base Tunnel, the longest tunnel in the world, built over 8,000 feet below the surface. The first idea for the tunnel was put forward in 1947, but construction only officially began in 1999 after years of approval and scouting for the perfect location.
The 73 different rock types that composed the mountain turned construction into a real challenge. Some rocks were as hard as granite, others as soft as sandstone, requiring different approaches and equipment so the whole thing would not crumble. Overall, workers had to excavate about 28 million metric tons of rock. The deeper into the mountain they got, the hotter the temperatures became, reaching as high as 115 degrees Fahrenheit since there was no natural ventilation.
The tunnel stretches for 35 miles from one end to the other, and workers used four massive tunnel boring machines, each around 1,400 feet long, which limited disturbance to the surrounding ground and helped produce a smooth tunnel wall. Even the world’s deepest basement belongs to the Sydney Opera House in Australia. The building goes as deep underground as it grows above ground, but the basement is not just the foundation; it is a parking lot. This unique parking garage penetrates 120 feet underground, or twelve stories deep, while most car parks are only four or five stories deep.
Since a normal rectangular parking space would have eliminated a bunch of possible parking spaces, engineers opened up a man-made cavern and designed a donut-shaped structure, what engineers call a double helix. The design shocked the engineering community for its innovative approach, but it worked. Today there is space for over a thousand cars down there. Some underground structures take up to an hour to reach, like a gold mine in South Africa that lies around two and a half miles below the surface.
The conditions are hard, but Milan Ladina, an Ecuadorian runner, even completed a half marathon there despite temperatures reaching 104 degrees Fahrenheit, humidity at 80 percent, and atmospheric pressure of 1. 4, comparable to what divers experience five meters under the sea. Some of the most remarkable underground discoveries were found completely by accident. Researchers in Scotland were testing new technology on the Isle of Arran, allowing them to explore what is buried underground without digging, a method called geophysical surveying.
They wanted to see how well their tools would work on the thick peat covering Machrie Moor. Instead, their equipment found something totally unexpected: a huge ancient circle. The machines detected a circular pattern beneath the thick layer of peat, and when the scientists turned the data into a map, they saw a large ring about 92 feet across, roughly the length of a passenger airplane. Inside the circle were twelve small marks arranged in a suspiciously organized way.
Researchers think they might be the holes where large wooden posts once stood, each post about 21 feet away from the next. There were two wide gaps in the circle, where two more posts could have once stood, meaning the original monument may have had around fourteen posts or stones. What makes the discovery even more surprising is that Machrie Moor is already one of Scotland’s most important ancient sites. Between around 3500 and 1500 BC, people built stone circles, standing stones, and burial sites in the area, and archaeologists had identified six main stone circles.
But nobody realized something incredible was hidden beneath the ground. The same survey revealed that one of the known circles, Circle 2, may have originally contained around fourteen stones instead of the seven or eight seen today. Researchers also discovered that some of the famous stone circles might not have started as stone monuments at all; some were originally made from wood, and later those wooden structures were replaced with stone. Several monuments at Machrie Moor line up perfectly with a natural opening in the hills called Machrie Glen, and around the time of the summer solstice, the longest day of the year, the sunrise would appear through this gap.
Those communities depended on farming, so the movement of the sun and the changing seasons were extremely important. Many centuries later, some of the circles were also used as burial places, with people both cremated and buried near the monuments. The newly discovered circle could have served a similar purpose, but researchers need more evidence to say exactly how it was used. The thick peat covering the landscape is wet and contains very little oxygen, conditions that can protect ancient materials from decay, so somewhere beneath the ground there could still be traces of the original wooden posts.
The idea that an advanced civilization could exist and then vanish without a trace has inspired scientists to ask a strange question: if a non-human species had built an industrial civilization on Earth millions of years ago, would we even be able to find evidence of it? This idea, inspired by a Doctor Who episode about reptiles called Silurians who were forced deep underground by rising temperatures, became known as the Silurian hypothesis. Climatologist Gavin Schmidt and astrophysicist Adam Frank decided to investigate. They looked for global effects that would leave a widespread mark, like residues from burning fossil fuels, mass extinctions, synthetic chemicals not found in nature, and traces of nuclear fission, the same kinds of things humans are currently leaving behind.
But this evidence is not easy to find. If humanity suddenly disappeared, a future civilization millions of years from now would struggle to find any remnants of our existence. Our industrial period has only lasted around 300 years, and we have not left any significant traces. The fossil record captures only some things, with one fossil emerging every 10,000 years on average.
Mountains rise, oceans change, and plate tectonics can easily wipe out evidence of entire civilizations. Even our cities cover less than three percent of the surface, making it easy to miss ancient city ruins. No prehistoric iPhone would survive millions of years, and finding fossilized remnants of a species is tricky. Scientists have looked into the past 380 million years and examined all suspicious events, but so far they have not found a clear match for a technological civilization.
They do not give up, though. Frank calls for more investigation, suggesting we study how modern industrial chemicals stick around in ocean sediments to help identify similar chemical traces in Earth’s history. The search for lost worlds has also produced plenty of legends that may never be proven. The most famous is Atlantis, first introduced in two of Plato’s works.
According to Plato, Atlantis was a highly advanced civilization that existed about 9,000 years before his own time, founded by beings who were half deities and half human. It was an island filled with gold, silver, and other precious metals, known for its architecture and technology. The Atlanteans became proud and believed they could gain control over any nation, launching a series of invasions and conquering many Mediterranean lands. But when they tried to enter Athens, the Athenians pushed back, and the Atlanteans were defeated.
Plato stated that the gods then got angry at the Atlanteans for becoming wicked, greedy, and immoral, and punished them by sending earthquakes that caused Atlantis to sink beneath the sea. Some people have tried to identify Atlantis with actual countries, suggesting it was in the Mediterranean near Spain or Italy, or in the Caribbean. In the nineteenth century, US Congressman Ignatius Donnelly wrote a book giving thirteen reasons why he thought Atlantis was more than a myth. In 1965, some people thought they found Atlantis when they discovered the Richat Structure, a massive 25-mile-wide dome in Mauritania, Africa, so big that you can see the whole thing from space.
Two astronauts flying over the Sahara Desert spotted this giant eye staring back at them and thought they had made the discovery of a lifetime, but there is no solid evidence linking the structure to Atlantis, which is believed to have formed from volcanic activity about 100 million years ago. Another theory suggests Atlantis was the island of Santorini, home of the Minoan civilization, which was destroyed by a huge volcanic eruption about 3,600 years ago. But the time when Plato said Atlantis was destroyed does not coincide with the time of Santorini’s eruption, so Atlantis still continues to be regarded as nothing more than a popular legend. The city of Ys, from Celtic Breton mythology, was said to tower over Douarnenez Bay in France’s Brittany region, the most wealthy city in the entire Atlantic, famous for its beautiful gardens and buildings.
Dahut, King Gradlon’s daughter, had a deep love for the sea and begged her father to build a city at the edge of the sea. Since the city was surrounded by the sea, it needed to be protected by a dyke equipped with floodgates, which could only be opened at low tide. The only one who had the keys to these gates was the king himself. One day, a handsome red knight arrived at the city but could not pass the gates.
Dahut was so taken by him that she stole the key from her father and gave it to the knight so they could be together. But the red knight turned out to be the prince of darkness, and he intentionally left the gate open to the raging sea. The wave soon swallowed all of Ys. King Gradlon escaped on his magical horse, but Dahut could not, and she turned into an evil mermaid who lured sailors into the sea.
Today, you can find a statue of King Gradlon riding his horse in Quimper, a city in Brittany, and locals believe that on days when the waters are calm, you can still hear the tolls of the city bells deep under the sea. The theory of Lemuria began in the mid-1800s when a few scientists suggested there was once a continent in the Indian Ocean south of modern-day Sri Lanka. British lawyer and zoologist Philip Lutley Sclater popularized the theory after finding lemur fossils in India and not in Africa, which was shocking because lemurs’ original homeland, Madagascar, is much closer to Africa. He proposed that a larger continent must have once connected the two, and that it eventually sank to the ocean floor.
He named it Lemuria. People who came after Sclater took the theory further, thinking Lemuria was also the home of an extinct race of humans called Lemurians who had four arms and enormous bodies and were ancestors of modern humans as well as lemurs. As new scientific discoveries were made on plate tectonics, evolution, and the study of DNA, the theories regarding Lemuria were debunked. The last of the legendary lost worlds is Agartha, a kingdom said to be located deep beneath the surface of the earth, where all four corners of the world are connected by paths and tunnels.
It is said there is a secret entrance hidden in the Gobi Desert, built by Agarthans themselves using advanced technology that cannot be detected by surface dwellers. According to some beliefs, Agartha exists to counterbalance the energies of those who live above the surface. Some even say that those who escaped Atlantis fled there to continue their lives inside the Earth’s core, while others think it is a land crawling with monsters. There is no need to be scared though, since modern science proved Earth’s core is not actually hollow and is a solid hot iron ball.
The search for lost civilizations continues on many fronts. On the island of Sardinia, stories persist of terrible giants who roamed the island 3,000 years ago, with people even talking about finding human skeletons over 13 feet tall, though nobody has ever shown anything to prove it. In 1974, over 5,000 pieces of broken stone artifacts were found in a part of the island called Monti Prama, but instead of being displayed in a museum, they were locked up in an underground vault for about 30 years. When they were finally displayed in 2005, scientists put the pieces together to find statues of 38 giant men standing 8 feet tall.
The statues were thought to have been made by the Nuragic people, who also built over 8,000 massive stone buildings on the island. In the Amazon, the Casarabe people lived for hundreds of years before vanishing around 1400 AD. The mysterious culture built a vast civilization that spread over 5,000 square miles and included about 450 geoglyphs, some as wide as 1,300 feet. They likely contained ceremonial buildings and could have hosted up to a million people.
Lidar scans in 2019 showed miles of raised roads and pathways and even pyramids over 70 feet tall, and they found 26 separate settlements, two of which were at least 250 acres each. It is not certain what happened to the Casarabe people; maybe European conquistadors drove them out, or maybe droughts forced them to leave. The Harappan civilization in South Asia, dating to about 3300 BC, had cities like Harappa and Mohenjo-Daro with baked brick houses, sophisticated drainage systems, and public baths. The region might have had over 5 million people, making it one of the densest regions at the time.
They invented a system of standardized weights, had connections stretching to the Middle East thanks to their metallurgy skills, and used seals to stamp clay on trade goods. But their language and script remain undeciphered, and no one knows exactly how their society worked. They did not flaunt social status with grand palaces or massive monuments; their largest buildings might have been granaries. Around 1800 BC, the civilization started to decline, possibly due to shifts in river patterns, and the Harappans packed up and moved towards more hospitable lands.
The Minoans on the island of Crete built palaces like Knossos, which was so complex with its multi-story buildings and elaborate hallways that it might have inspired the labyrinth myth of the Minotaur. Their engineering was so ahead of its time that even their drainage systems were more advanced than what many of us have today. In the Mesopotamian desert, the ancient city of Eridu, older than the first known civilization and older than the pyramids of Giza, was buried in the sands for over 2,000 years. Founded around 5400 BC, it was the city of the first kings and history’s first city according to the Sumerian King List, an ancient text on a clay tablet.
The Sumerians believed the gods created this city when they decided to settle on Earth. A new study showed that the Euphrates River served as the source of water for the entire city, with researchers mapping a network of artificial irrigation canals: 200 large main canals pulling water from the Euphrates, feeding another 4,000 smaller canals, bringing water to more than 700 farms. The city thrived until people abandoned it around 600 BC, possibly because the Euphrates changed its course and they lost their main source of water. In 1854, a British official named Taylor visited the area but was not impressed, finding only walls, drains, stone platforms, and pieces of limestone columns decorated with tiny mosaic cones, not knowing these boring mounds were hiding one of the oldest cities on Earth.
The first full-scale excavations took place around a century later, uncovering an unfinished step pyramid and layers of human life going back in time, including multiple rebuilds of the temple of Enki, the city’s main deity, rebuilt again and again for over 2,000 years, each new version bigger and more impressive than the last. By 1500 BC, the Sumerians had invented the seed plow, a tool that let farmers plow and plant seeds at the same time using oxen, and they produced the Sumerian Farmers Almanac, giving farmers advice on how to grow more crops with proper tilling and irrigation. Five thousand years ago, the Sumerians had already produced cuneiform, one of the first writing systems in history. And in another ancient Sumerian city, archaeologists found administrative tablets inside a state archive building made of mud bricks.
These clay tablets are the oldest solid proof of the world’s first empire, the Akkadian Empire. The tablets tracked everything: deliveries, spending, and inventory from fish to sheep to grains, fabric, and even gems. They also include population records with names and jobs of men, women, and children, an ancient version of a census. From these records, scientists found out that women played a key role in Akkadian society, with some holding powerful positions like high priestesses.
Eventually the city rebelled and gained its independence, and the Akkadian Empire’s 150-year rule ended.
