Nearly every city is built over an ancient site. The older the city, the greater the past that lies beneath. Sometimes, archaeologists find amazing things because they know where to look or doggedly followed rumors. But when it comes to rediscovering hidden history, most finds happen by accident. Unexpected treasure is the best.

10 The Corduroy Road

Under King Street in Waterloo, Ontario, runs a much older version of a road. The historic find was made in 2016 by a construction crew, which had been forewarned of a possible encounter with something resembling a row of logs. When that happened, they called in the archaeologists, who confirmed the discovery: It was a corduroy road dating from the time of the area’s earliest development.

Corduroy roads were constructed by placing logs across a path to ease passage across swamps or similar wagon-challenged areas. The one unearthed in Waterloo was probably built before 1877. Settlers used sand and packed the tree trunks tightly. While it made the crossing quicker and free of concern for becoming stuck in the mud, cart horses still faced injuries due to shifting logs. The partial path shows signs of extended use as well as diligent maintenance by the pioneers who used it.

9 The Roman Fresco

In 2016, a treasure was ironically discovered by the Museum of London Archaeology while scouting for a new office building. Found underneath 21 Lime Street was a large piece of wall, 2.4 meters (8 ft) long and 1.5 meters (5 ft) high. Archaeologists turned the facedown slab over and were stunned to find it was an elaborate, hand-painted fresco from Roman days. The artifact was almost 2,000 years old and showed a delicate nature scene mixed with some domesticity: feeding deer, trees, and birds as well as fruit and a vine-like plant growing around a candelabrum.

The fresco’s pigments were obtained from Spain, an extremely difficult thing to do in those days. This added to the museum experts’ conviction that the art piece had been commissioned by an elite family who spared no expense and possibly showed it off (and just how wealthy and fashionable they were) in their reception area.

8 The Gezer Site

During Biblical times, the Canaanite city of Gezer was a popular place to lay siege to. Whoever controlled Gezer owned the wealthy vein of the east-west trade route. The well-known archaeological site has been studied for decades but received an extra dimension in 2013: It’s sitting on another city.

Previously, layers beneath Gezer dated back to the tenth to eighth centuries BC, but the unknown second settlement proved to be far more ancient. The 14th-century-BC ruins most likely belonged to another Canaanite city, but it had some Egyptian flavor. Artifacts included a scarab amulet of Amenhotep III, better known to the world as the grandfather of Tutankhamun. Important Biblical-era cities are usually older than their official ages, but the Late Bronze Age roots of Gezer surpassed by far even that expectation.

7 Millennia Of Civilization

While Gezer covered up one city, Beirut stands on several. For 5,000 years, Canaanite, Phoenician, Hellenistic, Roman, and Ottoman civilizations rose one after the other, adding their own influences to this archaeological smorgasbord. The incredible time line came to light during excavations in central Beirut, meant to rebuild the city after its devastating civil war.

Among the finds were Roman ruins, including the city’s cardo maximus (main north-south street), quarters belonging to the Phoenician and Hellenistic cultures, a Canaanite mound, and a Byzantine trading place. One of the most incredible recoveries was a collection of mosaics. Placed side by side, they create a massive, 8,200-meter-long (27,000 ft) stretch of art. It was already believed that Beirut originated around 3000 BC, but this proved it.

6 Britain’s Oldest Writing

Britain’s oldest scribbles may reveal many firsts. In 2016, a cache of 405 wooden writing tablets were found beneath an underground river in the middle of London. These rare Roman communications were etched between AD 43 and AD 80, making them the earliest writing unearthed in the UK. Dating back to the year the Romans invaded Britain, the Latin phrases give new insights into London’s first community, a city that was erected by the invaders.

There’s a colorful plea for a loan, while another plank dishes out peppery business advice to someone a little too free with handing out loans. The first-ever written mention of London’s name, the country’s first IOU, and a tablet from perhaps the first school, with letters running the alphabet, were also found. Soldiers, judges, and businessmen all left messages behind that will now help researchers to better understand this early urban society.

5 The Ehecatl-Quetzalcoatl Temple

In Mexico City, archaeologists didn’t bat an eyelid when ancient pottery and eight human skeletons were found beneath a supermarket in 2016. What excited them, though, was the unexpected sight of a temple. For years, shoppers remained unaware that beneath their feet slept a sacred site dedicated to the Mexica-Tlatelolca people’s wind deity, Ehecatl-Quetzalcoatl. It won’t match the grandeur of other ancient temples of the world, but it remains a remarkable find.

The temple is basically a round platform, 1.2 meters (4 ft) high and 11 meters (36 ft) in diameter, with most of its original white stucco undamaged. To honor their god, priests of the pre-Hispanic city of Tlatelolco left gifts: bird parts, such as bones and duck bills, statues of monkeys, obsidian, cactus spines, and even a human baby. The 650-year-old platform is in the middle of a mall development scheme but will be preserved so visitors can view it.

4 The Malta Tunnels

The Mediterranean island of Malta holds a subterranean secret. For centuries, it was claimed that the Knights of Malta, a Christian military order, constructed an elaborate underground complex while fighting Muslim forces on Malta. In 2009, construction surveyors found tunnels beneath the capital of Valletta. The network dates to the 16th and 17th centuries, when the order occupied the island.

Experts believe the tunnels are a plumbing system that blessed the embattled Valletta with fresh drinking water and a sewage system light-years ahead of its time. The well-built passages, containing centuries-old metal valves and pipes, are wide enough for a person and allowed the knights easy access to do maintenance. Other rumors, such as secret carriageways and an entire underground Valletta, are, according to archaeologists, not impossible but still lack evidence.

3 Antidepressant Factory

In 2007, drought had evaporated much of Lake Kucukcekmece in Turkey. Archaeologists zoomed in when the exposed shores promised a slice of history, and they weren’t disappointed. They soon uncovered a large-scale medicine factory. Tools like mortars and pestles, cooking pots, spatulas, and medical devices surfaced. What confirmed the nature of the site was a haul of 700 vials. Each contained a remedy of some sort. Two were analyzed and turned out to be 1,400-year-old drugs for depression and heart ailments.

The vials represent the largest stockpile of ancient medicine and were recovered from the burned remains of the factory along with the preparation tools. The destruction is the first indication that a suspected onslaught in AD 646 by Istanbul’s enemy, the Avar Empire, did occur. More artifacts could be in the lake’s remaining waters, but nuclear and industrial pollution makes exploration too risky.

2 Kublai Khan’s Palace

Chinese historians suspected Kublai Khan’s palace once stood near the current location of Beijing’s Forbidden City. Historically speaking, the palace has always been a sought-after prize. In 2015, during maintenance efforts in the Forbidden City, tile and porcelain fragments from the Yuan dynasty (1271–1368) were discovered. This drew immediate scientific attention because the tiles were from the era during which Khan ruled China. No longer did researchers look for the long-missing Mongol conqueror’s palace in the vicinity of the Forbidden City but rather directly beneath it.

Digging deeper, the foundations of the dynasties that followed, the Ming and Qing, came to light. Archaeologists now believe that the Ming dynasty tore down every brick of Kublai Khan’s royal buildings and constructed the famous gardens and palaces of the Forbidden City over it.

1 The New York Vaults

In 1965, an electricity company stumbled upon an underground tomb. Due to bad record-keeping, the location of the skeleton-stuffed vault disappeared. Then, in 2015, during an excavation to switch a 100-year-old water main under Washington Square Park, the gory resting place revealed itself once more. This time, it came with a surprise: a twin vault nearby.

Inside the second tomb rested 20 neat wooden coffins. The first was a jumble human bones. The 200-year-old chambers are 4.6 meters (15 ft) wide and 8.2 meters (27 ft) long, with tall walls and arched ceilings. Wooden doors lead to unknown destinations.

Washington Square Park used to be a grave site. After the Civil War, society’s unwanted received unmarked graves, and the dead from a yellow fever epidemic were once buried there. The twin vaults could belong to the 18th-century Cedar Street Presbyterian Church, but they kept no records, so even that remains uncertain.

Scientists are constantly making new discoveries about ancient tombs and monuments, usually to the effect of what they were used for. Some of those discoveries, however, involve secret passageways that hide secrets about the ancient world. Here are ten hidden passages that were found beneath ancient monuments and heritage sites you never knew existed!

Related: Top 10 Jaw-Dropping Hidden Spaces In Paris

10 Tunnel in the Great Pyramid of Giza

Most people are aware that the pyramids are home to networks of tunnels that take you between the various chambers. However, that’ s not to say that all the tunnels have been discovered or even that scientists know what they were all used for.

One of the more recent underground tunnel discoveries relating to the ancient world was an underground tunnel found not inside but underneath the Great Pyramid of Giza. The tunnel was discovered in March 2023 and is about 30 feet (9 meters) long. It sits close to the main entrance of the pyramid and was picked up using ultrasonic and radar testing.

As of now, scientists still aren’t sure what the tunnel was used for. However, one theory is that it may have been built to help distribute the weight of the pyramid more evenly. More testing will be needed to see if they can solve the mystery.^[1]

9 Teotihuacan

The Great Pyramid of Giza isn’t the only pyramid with a hidden tunnel beneath it. Another pyramid that holds secrets buried deep underground is Teotihuacan’s Pyramid of the Moon.

This pyramid is thought to mirror the great monuments of Teotuhuacan and perhaps represent the underworld. The tunnel is about 33 feet (10 meters) deep and runs from the Plaza de La Luna, the square near the pyramid, to below the pyramid itself.

Although scientists still aren’t sure what the tunnel was used for, they do know that the Pyramid of the Moon was a temple where human sacrifice was performed. So perhaps the tunnel had a similar sinister purpose. It will take more digging and testing to find out for sure.^[2]

8 Talatal Ghar

Talatal Ghar is an old military base and palace dating back to the 18th century. It’s located near Assam, India, and was built during the Ahom period in the country.

At first glance, Talatal Ghar is just another army base and 18th-century palace. However, looking a little closer, you’ll quickly unearth the base’s secrets. You see, Talatal Ghar has two secret tunnels that are built around three stories underground.

One tunnel is nearly 2 miles (3.2 kilometers) long, while the other tunnel is almost 10 miles (16 kilometers) in length. The shorter tunnel connects Talatal Ghar to the Dhikow River, while the longer tunnel leads to the nearby Garhgaon Palace.

Unlike some of the other secret tunnels hidden beneath historical sites, scientists actually know the purposes of these passages. The Ahom period was a period of war, and as a result, these tunnels were used as escape routes from the palace during the Ahom wars.^[3]

7 Chand Baori

Another Indian heritage site that’s home to secret tunnels is Chand Baori. Chand Baori is a stepwell, or a well or pond with a series of steps leading down to the water, located in the state of Rajasthan.

This type of stepwell was actually pretty common throughout India and was used as a place to gather water, cool down on hot summer days, or hold religious rituals. Many stepwells were built near forts and palaces to make them easy for people to access. The stepwells were popular from around the 7th century until the 18th century.

What’s really interesting about these stepwells, however, is that there was often more to them than meets the eye. Many of them actually provided secret access to an underground tunnel network throughout the Rajasthan state, used to serve as a transportation system in case of an emergency.

Chand Baori is one of these stepwells and grants access to the tunnel network, which extends to various other local monuments and heritage sites, including Amber Fort.

Despite all the intrigue of the stepwell tunnels, there’s some debate as to whether they really do date back to the 8th century. Some historians argue that these may have been built more recently, in the 20th century, in order to draw tourists to the area. It’s up to you to decide which story you believe.^[4]

6 The Colosseum

The Colosseum draws thousands of visitors each year, providing a glimpse into ancient Roman culture and some of their more brutal customs and traditions. While tourists have long been free to wander through the Colosseum and get a feel for what it might have been like to watch a game in this ancient monument, they haven’t always been able to go beneath the Colosseum.

The Colosseum had a network of tunnels and passageways hidden underground where gladiators would prepare for their fights. These passengers were invisible to spectators and have remained invisible to tourists for a long time as well.

In 2021, however, several of these hidden underground passageways were restored, making it possible for tourists and scientists alike to learn more about them. So perhaps it’s time to plan a trip to Rome to explore some of the ancient world’s hidden passageways.^[5]

5 Manzana de las Luces

Manzana de las Luces is an old Jesuit religious complex that sits in San Telma, Argentina. The complex was built in the late 1500s and was part of a mission to promote Christianity in the New World.

Despite their lofty mission, the Jesuits weren’t welcome in Argentina, with indigenous groups threatening them with armed conflict. To protect themselves, the Jesuits at the Mazana de las Luces mission began to create a network of tunnels beneath the church that extended out to other churches around the city. The idea was to give them an escape plan in the event that the natives launched a serious attack.

Interestingly enough, these tunnels were never properly documented, making it challenging for scientists to uncover the true extent or purpose of the tunnels. The tunnels were originally found in the 1900s during a construction project, and other tunnels suspected to have been part of the network have been found over the years during other construction projects.

Sadly, many of these tunnels have since been lost to time. However, tourists can still check out a short section directly under the Manzana de las Luces mission.^[6]

4 Chauvin de Huantar

Chavin de Huantar is an ancient archaeological site located in the highlands of Peru. It is believed to have been built by the Chavin culture, which flourished between 900 BC and 200 BC. The site is known for its impressive architectural features, including a complex network of underground tunnels that were used for ceremonial purposes.

The hidden tunnels of Chavin de Huantar are an important part of the site’s history and significance. The tunnels were built using sophisticated engineering techniques and were designed to channel water and connect different parts of the site. They also played a role in the religious practices of the Chavin culture, as they were used for ceremonies and possibly as a way to communicate with the gods.

The passageways were discovered in the 1940s by Peruvian archaeologist Julio C. Tello. Since then, they have been extensively studied and explored by archaeologists and other experts. Today, Chavin de Huantar is considered one of Peru’s most important archaeological sites and a popular tourist destination. Visitors can explore the underground tunnels and other architectural features of the site, including the Temple of Chavin, a massive stone structure decorated with intricate carvings and sculptures.^[7]

3 Red Fort

The Red Fort is a Mughal Empire-era fort that sits in the Old City in Delhi, India. This fort is a UNESCO World Heritage site and attracts many visitors each year looking to learn a bit more about the country’s history.

Recently, however, scientists discovered that there was a secret hiding beneath the Red Fort. The tunnel, which connects to the Delhi Legislative Assembly, was discovered in 2021. It seems to have once been a tunnel used by the British to move freedom fighters around the city. Still, the exact history and purpose are up for much debate, and historians haven’t been able to find detailed records about it.

What’s more, much of the tunnel has been destroyed in recent years. Thanks to the construction of the Delhi Metro and sewer system, the full tunnel no longer remains intact. Despite this, Delhi officials have hopes of restoring at least a small section of the tunnel and making it available to the public to check out.^[8]

2 Taposiris Magna

The Taposiris Magna is an ancient Egyptian city that sits outside modern-day Alexandria. This ancient city is home to ruins, temples, and unique historical sites. However, it’s also home to a recently discovered network of tunnels that sits below one of the temples in the village.

The tunnel network is more than 13,770 feet (4,200 meters) long and is about 6.5 feet (2 meters) tall. The tunnel is hidden about 65 feet (20 meters) underground and seems to be an exact replica of the Eupalinos Tunnel in Samos, Greece, which was used to move water.

This is most likely due to the fact that the tunnel dates back to the Ptolemaic period when Egypt was ruled by Greece. Scientists are still excavating at the tunnel to learn more about it, but as of now, it’s also thought to have been built to move water around the ancient city.^[9]

1 Royal Palace of Naples

The Royal Palace is a palace in Naples, Italy, that was owned by Ferdinand II of Bourbon during the 18th century. However, beyond the riches and treasures hidden within the castle’s walls are far more secrets beneath the Palazzo itself.

You see, beneath the palace lies a network of tunnels built by King Ferdinand II in the 1800s due to fear of a revolutionary uprising. The tunnels are huge, designed to fit military troops and horses and lead them from the barracks to the Royal Palace.

Interestingly enough, the tunnels are home to much more modern artifacts than you might think based on when they were built. During World War II, they were used as bomb shelters as well as a place to smuggle contraband vehicles before they were closed off in the 1950s. As a result, many of the artifacts within the tunnels date back to this more modern period.

The tunnels were rediscovered by accident when scientists conducted seismic testing on the area. Today, the tunnels can be visited by tourists, often as part of a tour of the Royal Palace of Naples.^[10]