Pohnpei is an island in the Pacific Ocean that is part of the Federated States of Micronesia. It is perhaps best known for the remains of an ancient city, Nan Madol, located off the southeastern shore of the island and constructed in a lagoon. Some of the structures here date back to the eighth and ninth centuries AD, but archaeological research has shown that the site was already inhabited around two thousand years ago.

Nan Madol has attracted a lot of interest over the years. An early mention is in Abraham Merritt’s novel The Moon Pool (1918-1919), originally published in serial form. Merritt’s novel is part of the “lost world” genre that was popular at the time and included authors such as Edgar Rice Burroughs, H.P. Lovecraft, Jules Verne, and Arthur Conan Doyle. These novels and serialized stories were set in exotic but real places that fired the imagination and transported the reader to worlds outside common experience.

In The Moon Pool, Merritt describes a fantastical alien other-world that was entered through a portal in the central tomb of Nandowas (or in the orthography of the day: Nan-Tauach), in Nan Madol. He references the popular work of F.W. Christian (1899a), who had actually visited Pohnpei and Nan Madol. Merritt’s character Throckmartin states, “(w)e came to the conclusion that there must be a passage-way between Ponape and Nan-Tauach known to the natives – and used by them during their rites” (p. 24).

A Pohnpeian legend relayed as part of the Pacific Storytellers Cooperative describes “another kingdom under the ocean. Supposedly there was an escape tunnel beginning at the center of Nan Madol, boring down through the reef to exit into the ocean” (e.g. Kikuchi). Other oral histories describe tunnels on various islets of this ancient site, as on Dorong Islet: “(t)here are several holes beneath the land that run from the channel outside of Lehnkei. But there is one hole in the center. It is said that it goes underground and appears far away in the harbor of Pahn Nakapw” (Thompson et al. 2015).

This same idea is repeated on contemporary websites such as Mysterious Universe, often couched as local lore but with a hint that perhaps this mysterious place actually contains features yet to be discovered, such as “(t)he locals claim that beneath the city lie vast networks of tunnels and tombs, and that this was once the land of actual giants and the stomping grounds of various spirits” (Swancer 2019).

Swancer subtly reinforces the mysterious aura of Nan Madol by stating there has been little scientific work at the site and repeats stories about the tragic consequences of disturbing the site, e.g. Kubary lost all his notes and artifacts when his ship sank after working on the island or a German governor mysteriously died after entering the site at night.

Still others of a more esoteric/New Age persuasion continue to echo the existence of tunnels under Nan Madol: “(u)nderground tunnels are said to connect Nan Dowas to several of the larger buildings outside the complex. It is believed that some of these tunnels go beneath the reef and exit underwater to caves near Madolinihmw Harbor, which can be seen while scuba diving, but are too clogged for a person to swim through” (PerceptiveTravel.com). 

An introduction to Nan Madol

Any visitor to Nan Madol would characterize the site as amazing. It is one of those ancient, abandoned places in a far-off corner of the world that is shrouded in mystery, associated with ghost stories, and of a monumentality that exhibits a complex megalithic architecture as impressive as Machu Picchu in Peru, the pyramids of Egypt or the temples of Angkor Wat. It captures the imagination, with one early western visitor christening the site as the “Venice of the Pacific” (O’Connell 1841).

Nan Madol is among the largest archaeological sites in eastern Micronesia. In 2016, it was inscribed onto UNESCO’s World Heritage List because of its outstanding characteristics, while at the same time included on the list of World Heritage in Danger because it is subject to the deleterious effects of an aggressively changing climate, high sea stands, and a nearly impenetrable and rapidly expanding occupation of mangrove vegetation (Beardsley et al. 2015).

The unique qualities of Nan Madol – its off-shore location, its 100+ artificial islets separated by navigable canals, and its monumental stone and coral architecture – have attracted the attention of scientists, archaeologists, and even missionaries since at least the nineteenth century, contradicting the claim by Swancer that there has been little scientific research at the site.

Early visitors and missionaries include the likes of Clark (1852), and Gulick (1857); early scientific researchers (eg. Kubary 1874); the systematic archaeological studies of the German Expedition (Hambruch 1911 and Sarfert 1911-1912); the succeeding Japanese research (e.g., Muranishi 1942); and, beginning in 1963 with the Smithsonian project (Long 1965), a whole host of archaeological and scientific research (e.g., Ayres and Haun 1978, Athens 1980, McCoy et al. 2016). There are more, naturally, just not listed here.

Pohnpei is one of three high volcanic islands at the eastern end of the Caroline Islands in Micronesia. It is small, a mere pinprick on any map of the world, with a land area of 334 km². The island is mountainous, tropical, and has an extremely high annual rainfall (averaging 4.65m annually) that feeds large rivers, dense jungle, and a cloud forest. At 6 degrees north of the equator, Pohnpei is surrounded by a barrier reef, which creates a large lagoon that supports several smaller off-shore islands.

The island was settled roughly 2,000 years ago, as indicated by evidence of forest clearance by fire and subsequent soil erosion (Haun 1984), and the presence of pottery fragments off the shore of the lagoon island of Temwen (Ayres 1993). Nan Madol was established roughly a millennium after initial settlement, in Madolenihmw municipality, on the southeastern side of the island. It played a central role in the growing political complexity of the central Pacific region, with its power and position reinforced by 83 hectares of monumental architecture spread across a shallow reef platform.

The megalithic structures that rise from each artificial islet have walls some 6 to 7 or more meters high and at least 2 meters wide at their bases. Each islet is constructed with basalt and coral boulders topped by lengths of columnar basalt placed in header-stretcher patterns; building walls are primarily double-walled constructions with wide bases and narrow tops, and cores of packed coral rubble.

An estimated 2000 tons of volcanic rock were incorporated into the site every year for at least three to four centuries, and all of it moved and placed without benefit of pulleys, levers, metal tools, or wheels. Ayres and Sheller (2002) estimate the total mass of construction materials consisted of 300,000 m³ of stone, or 0.5 to 0.75 million metric tonness. It is likely an equal or greater amount of coral was recruited for islet construction and wall fill.

Among the most notable (most visited and probably most photographed) islets is Nandowas, at the eastern corner of Nan Madol. Its architecture is more elaborate than any of the other islets, with walls some 8 meters high, roughly 3 meters wide at their base, and consisting of columnar basalt placed on top of colossal (megaton) stone boulders.

As the mortuary islet and burial place for the rulers of the Saudeleur Dynasty, Nandowas was the religious and ceremonial center of the site. There are three massive tombs on the islet, with the central tomb placed within an inner enclosure—it is this tomb that plays a key role in Merritt’s The Moon Pool and other stories about tunnels under the site.

Looking for tunnels

Now, about those tunnels. An underwater survey in Nahkapw Harbor, adjacent to Nan Madol, found no indication of tunnels in the topography of the reef (Ishimura et al. 2014). The team happened to be investigating yet another myth of a pre-Nan Madol/“first city” on the reef that sank into the sea.

This myth basically stated that this “first city” sank because of its weight, and as a result caused the roof collapse of a submarine cavern within the reef creating a “blue hole” or hole in the reef, and further, that the ancient city of Nan Madol was then built on top of this “blue hole” – essentially creating a tunnel from Nan Madol into the harbor.

Archaeological investigations in the central tomb on Nandowas, another proposed location of a tunnel entrance, indicated it is simply a burial vault into which highly prominent individuals were laid to rest with their grave goods and personal adornment.

Some of the grave goods had been removed by early scientists like Kubary (1874), though he never excavated; later researchers chose to leave the other tombs and their associated grave goods and beads undisturbed, out of respect for the dead and their living descendants.

As for the possibility of a tunnel from the central tomb linking the main island of Pohnpei? There is no indication of any opening, secret or otherwise, other than the entry at the top of the vault. The tomb is lined with a cribbing of columnar basalt, which includes the floor.

Christian (1899b) even notes that Kubary, during his investigations of this central tomb, used the structure as “a developing-chamber for his negatives”. Christian’s own explorations into the central tomb describe the interior as (1899a):

about 8 feet in depth, roofed in with six enormous slabs of basalt. The flooring was paved by some heavy basalt blocks, which we had great trouble lifting away. Below this was a layer of soft vegetable mould, thickly matted with a tough root-growth that made excavation somewhat troublesome.

At no point did Christian observe a tunnel entrance in this tomb. More recent archaeological investigations at Nan Madol make note of channels or conduits on various islets, but these are associated with water flow for interior aquaculture pools (clam farming on Dorong Islet) and eel feeding rituals (on Idehd and Dau Islets).

On Dorong, a number of tunnel cavities or culverts built into the islet architecture have been reported, all of which functioned to allow freshwater to feed into the interior reef pool; at least one culvert associated with the eel, a sacred animal, was identified on this islet (Thompson et al. 2015).

Associated oral traditions link Dorong with stories about tunnels running from the site center to the harbor. Both Idehd and Dau Islets also have holes built into their architecture and associated with the eel; Idehd Islet was the location for rituals dedicated to the eel (Thompson et al. 2015):

When this ceremony began, they called it the Prayer of Nahnisohnsapw, which they performed for the Great Spirit. But the symbol of this prayer was a salt water eel whose name was Nan Samol. Nan Samol lived under the island of Idehd, and there is a hole where it used to appear and was visible.

None of the channels or culverts on Dorong, Dau, or Idehd Islets, were underground passages that extended from Nan Madol to the main island of Pohnpei, or even connected one islet to another. They were, instead, channels built into the islet architecture that allowed for the free flow of water into a reef pool or hole, used to serve very specific purposes – as in-flow for a clam aquaculture pond or as part of ritualized ceremonies dedicated to a revered animal.

Conclusion

The claim for a network of tunnels under the ancient city of Nan Madol, Pohnpei, seems to have its origins in traditional oral histories about passages from the center of the site to the adjacent harbor, imaginative tropes of “lost world” novels and serialized stories where romanticized adventures begin at a known/authentic place and quickly veer into fantastical worlds of aliens, prehistoric creatures, and supernatural tribes, and New Age/esoteric tenets published on websites dedicated to global mysteries.

However, scientific studies completed at the site since the nineteenth century do not support this claim. In other words, there is no evidence for the existence of a tunnel network under Nan Madol. There may be some confusion stemming from archaeological studies that use terms like “tunnel” to describe the culverts or conduits built into the site architecture.

While perhaps an unfortunate application of the term, these culverts (or “tunnels”) were integrated into islet architecture, not drilled through the reef, and none are large enough to allow the passage of a person. There simply is no evidence for tunnels or passages that extend from the site to the main island of Pohnpei, or for that matter to other worlds.

It is for these reasons we rate the overall claim as false.