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"Venice of the Pacific" - The ruin consists of 92 artificial islets built on top of coral reefs, which are linked by a network of canals, giving it the nickname “Venice of the Pacific.”

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The meaning of the real name - "Nan Madol" means "the space in between," which references the canals, yes, but it also calls upon the city’s history and reputation of hosting ghosts.

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The million dollar question - Why would someone build a city in the middle of the ocean, so far away from any other known civilization?

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One thing is for certain - It’s an engineering wonder, built entirely of giant basalt slabs in a time where there was nothing close to our modern tools.

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Impressive scale - The massive basalt walls are reportedly 25 ft (7.6 m) tall and 17 ft (5 m) thick in some places.

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Megalithic architecture - Carbon dating indicates that some of the structures are around 900 years old, but the islets themselves date even further back to the 8th and 9th centuries CE.

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Humans were there earlier -

Evidence of the earliest human activity dates back to the first or second century BCE, according to Atlas Obscura. Little is known about the ancient race who inhabited the area.

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Where did all that basalt come from? - The basalt stones are reported to have come from the opposite side of Pohnpei, from a volcanic plug where magma had hardened within the vent of an active volcano.

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How was it transported? - Modern archeologists have no idea how the massive stones were moved from one side of Pohnpei to the other, then stacked so high, considering the primitive technology that would have been available at the time.

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It rivals the work of the pyramids -

The effort required to build the megalithic structures would have rivaled that of the Egyptian pyramids, Oddity reports, as the rocks had an estimated total weight of 750,000 metric tons.

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Theories of transportation - Experts have suggested that rafts may have been used to transport the huge rocks to the reef, but there are still no theories for how they were originally moved from their far quarries or how they became those impressive structures.

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The location alone is baffling -

Why would anyone choose a location so far from civilization, on a coral reef, to drag all of those rocks to?

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The strange islets - The 92 islets are very similar to each other and geometrically shaped, but no one knows why.

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Mythology enters - Myth filled the gap that science can’t explain, and Pohnpeian legend says the city was constructed by twin sorcerer brothers, Olisihpa and Olosohpa.

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A site for worship - The brothers wanted a place to build an altar so that they could worship Nahnisohn Sahpw, the god of agriculture, which is somewhat ironic since the islands are not fit for agriculture.

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How did they move the stones? - The legend says the brothers performed rituals and used the help of a flying dragon to levitate the massive basalt and create the islets of Nan Madol.

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Naturally, they ruled the city - Olosohpa eventually became the first Saudeleur, marking the beginning of a dynasty that went on to rule Nan Madol until about 1628.

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When sorcery makes sense - Most Pohnpeians reportedly still believe that the ancient city was the work of sorcery, as no other viable theory for how humans moved 750,000 metric tons of basalt has surfaced.

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A sacred site - However it came to be, it is recognized as a sacred site founded by the Saudeleur dynasty, which was once populated by chiefs and priests, as well as commoners to serve them. Pictured is the Saudeleur dynasty tomb.

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Political seat of power - The Saudeleur rulers mandated local chieftains to reside in Nan Madol so they could monitor their activity and maintain control.

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Several uses for the islets - While most of the islets were residential areas, some were specially dedicated to food preparation, coconut oil production, or canoe construction, Atlas Obscura reports.

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It had quite a significant population - It’s estimated that the population of Nan Madol was more than 1,000 at a time when Pohnpei’s entire population barely reached 25,000.

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No food or water - The subjugated Pohnpeians had to bring food and water to the city, as there were no means to grow crops or collect fresh water on the reef.

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A logistical problem of surviving - This problem may have been what led to the abandonment of this impressive city.

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Contesting stories of how it ended - There are many tales of how the Saudeleur reign ended, but all of them attribute it to the legendary warrior Isokelekel in the 15th century, who, it’s said, implemented a new system of tribal chiefdom.

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It's sometimes called "the ghost city” - The mystery of the ancient city’s origins and purpose has naturally inspired quite a few legends involving spirits and ghosts. Some are scared to visit, while others go precisely for the spook.

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Inspired H.P. Lovecraft -

Howard Phillips Lovecraft was a famed American writer whose fictional sunken city of R’lyeh, featured in his Cthulhu mythos, was apparently inspired by Nan Madol.

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'Call of Cthulhu' - His short story mentions the real island of Pohnpei and uses the mythology of Nan Madol in his description of "The nightmare corpse-city of R’lyeh" which was "built in measureless eons behind history."

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It's a relatively new protected site - In 2016, Nan Madol was added to the list of UNESCO World Heritage sites.

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But it's also in danger -

The ruins are threatened by climate change, rising sea levels, encroaching mangroves, and the temperamental Pacific weather, earning it a place on the World Heritage in Danger List as well.

See also: Mysterious ancient civilizations you've probably never heard of

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