Basilica Cistern

Hidden under the city of Istanbul, Türkiye, are hundreds of ancient silos that once stored and provided water to ancient residents. The largest of these is the Basilica Cistern, so massive that it is known as the “Sunken Palace”. Basilica Cistern was built in 532 by Eastern Roman emperor Justinian I to solve the city’s drought problem. The bunker is 138 m long, 64.6 m wide, has an area of nearly 10,000 m2 and can hold up to 80,000 m3 of water.

The process of building the Basilica Cistern was very elaborate with 336 marble columns supporting the cellar. According to some experts, most columns are recycled from old buildings. The bunker was no longer used after the 10th century because maintenance was too costly and labor-intensive. Over the years, tons of mud covered the cellar until it was rediscovered and reinforced several times, starting in the 18th century.

Gadara water canal

The Gadara aqueduct was built to supply water to a cluster of 10 Roman-Hellenistic cities, today in Syria and Jordan. This amazingly engineered water channel belongs to the Roman Empire and was likely influenced by the Persians.

The 170 km long canal system is not only the longest ancient underground water channel in the world but also the most complex. The project was built with very high precision. The slope of the underground channel is extremely small, decreasing only 30 cm per kilometer. The Gadara Canal carries fresh water from sources 100 km away to the city’s western suburbs. When completing construction of the aqueduct system, workers excavated more than 600,000 m3 of limestone, equivalent to more than a quarter of the total volume of the Great Pyramid of Giza.

Derinkuyu underground city

Beneath the cobblestone streets of Derinkuyu city lies a network of ancient tunnels and chambers that could have sheltered 20,000 people. Located at a depth of more than 85 m and consisting of 18 floors, this is the world’s largest underground city ever discovered.

The structure was rediscovered in 1963 when a local man kept losing his chickens. After noticing a flock of chickens falling into a crack during house renovation, the owner found a dark passageway leading to the complex. There are hundreds of houses in the area that also have hidden entrances leading into the underground urban area. Interspersed among the nooks and crannies of the complex are rooms that were once used as meeting places, barns, kitchens, warehouses, and small prisons. The building even has an efficient ventilation system that allows fresh air to circulate deep within the labyrinth structure.

Derinkuyu underground city mainly serves as a shelter during war or difficult times. The date of the city is still debated among scholars, but some estimates place the construction 2,800 years ago.

Margate Shell Caves

What makes the seaside town of Margate in Kent, England, so special is the presence of the Margate Shell Caves. In 1835, the local schoolmaster, James Newlove, wanted to build a pond in his garden. While digging, his shovel fell into a large crack under a rock. He used a rope to bring his son down to pick up the item. However, when he turned up, the boy told about the tunnels decorated with seashells below.

Subsequent excavations revealed a spectacular cave containing more than 4.6 million marine shells mounted on a 600 square meter mosaic. What makes the Margate shell cave so mysterious is that experts have no information about this structure. They do not know exactly when it was built, by whom and for what purpose.

Rome’s tunnel network

Beneath the streets of Rome, Italy, lies a network of tunnels and quarries that date back to the city’s earliest times. Initially, these were tunnels for ancient Romans to exploit stone to build the city. The city later expanded and was built above the tunnels. Later, when stone mining ended, the ancients began to use this underground network as catacombs, to grow mushrooms and as a drainage system. During World War II, people also used them as bomb shelters.

“There are hundreds of kilometers of tunnels running beneath the city and its suburbs. Parts of the network are well understood and open to visitors, while other parts remain underexplored. Perhaps there are also Many catacombs are lost,” said Adriano Morabito, president of the Roma Sotterranea association.