Off the coast of a remote Micronesian island lay the ruins of a once-great city of man-made stone islands that represent the remains of megalithic architecture on an unparalleled scale in Micronesia—and inspired the city of R’lyeh in H. P. Lovecraft’s Cthulhu Mythos. 

Evidence of the earliest human activity dates back to the first or second century BC. The construction of artificial islets started probably about 8th and 9th century AD. However, the megalithic structures were built in period of 12th to 13th century, about the same time as the stone construction of the Cathedral of Notre Dame in Paris, or Angkor Wat in Cambodia.

The complex of Nan Madol is constructed on a series of artificial islets in the shallow water next to the eastern shore of the Pohnpei island. The site encloses an area approximately 1.5 km long by 0.5 km wide and it contains nearly 100 artificial islets.

Nan Madol seems to have housed the ruling elite caste of Saudeleur dynasty. It was a political and ceremonial seat of power. As a means of control of their subjects Saudeleur dynasty had succeeded in uniting the clans of Pohnpei. The rulers forced local chieftains to leave their home villages and move to the city where their activities could be more closely observed.

Most of the islets served as residential area, however some of them served special purpose, such as food preparation, coconut oil production or canoe construction. Madol Powe, the mortuary sector, contains 58 islets in the northeastern area of Nan Madol. The centerpiece of the whole complex is the royal mortuary at the islet of Nandauwas, with its 7.5m high walls surrounding the central tomb enclosure.

The population of Nan Madol was probably more than 1000 at a time when whole population of Pohnpei barely reached 25,000. There are no sources of fresh water or possibilities to grow food on Nan Madol so all supplies had to be brought in from the mainland. The population of the city probably included a large number of commoner servants.

Nan Madol is the biggest center of the culture which left numerous other megalithic structures scattered on neighboring shores and on main island of Pohnpei; it all can be found in the area of about 18 square kilometers.

According to local legend, the stones used in the construction of Nan Madol have been flown to the location by means of black magic. Archeologists have located several possible quarry sites on the main island, however the exact method of transportation of construction material is still not determined.

Lovecraft used the story of the ruins as the basis for his R’lyeh, a fictional sunken city and home to Cthulhu, appearing in the short story “Call of Cthulhu”: “The nightmare corpse-city of R’lyeh … was built in measureless eons behind history by the vast, loathsome shapes that seeped down from the dark stars. There lay great Cthulhu and his hordes, hidden in green slimy vaults … until the end.” 

The real island of Pohnpei is also mentioned in the story.

Nan Madol had been abandoned by the time the first Europeans arrived, early in the 19th century, most likely declining at the time of the fall of the Saudeleur Dynasty in about 1450. Some have claimed that the ruins are the lost islands of Lemuria, although there is no scientific backing for this claim (or, for that matter, for the existence of Lemuria at all).