The Non-Mystery of Nan Madol

by Brian Dunning
January 3, 2023

On the shore of an idyllic island in Micronesia lies one of the great ancient megalithic structures in Oceania, one that surprisingly few people have heard of. Great quantities of huge rocks were brought from far away and used to construct artificial islands over a flat reef, some 1.5 km long and .5 km wide. Called Nan Madol, it is — unfortunately — best known for a difference of opinion concerning its origin. While archaeologists and historians credit the people who lived there at the time and who left it littered with evidence of their construction, habitation, and use, a subculture insist that it is proof of ancient alien visitation, as if only extraterrestrials had the ability to move and stack rocks.

Temwen is a small three-square-kilometer island adjoining the much larger island of Pohnpei, formerly known to the English speaking world as Ascension, a rocky volcanic island with greenery-covered mountains reaching almost 800 meters high. Much of Temwen is surrounded by coral reef shallows, and upon the reef along its southeastern edge is where Nan Madol was constructed. There are some 92 of these artificial islets, mostly constructed in a sort of log cabin style made with long basalt columns, with walls and floors filled with coral debris.

Like other Pacific Islander cultures, the Pohnpeians had no written language, so no recorded history exists telling us what Nan Madol was used for. There are tombs for several kings (called the Saudeleur), and oral histories and archaeology gives us a decent picture of the rest. There were dwellings for priests, buildings for food preparation, and mostly ritual sites with supporting infrastructure. It is mostly surrounded with a seawall, the weather-facing cornerstone of which is a single basalt block that is by far the largest anywhere at the site, estimated to weigh some 50 tons. This massive weight is what has, more than anything else, persuaded amateur alternative historians to dismiss the island's true anthropology and insist that only a supernatural force, like aliens with rock-levitating technology, can explain its existence.

For a roundup of these claims, one need turn only to the notorious TV show Ancient Aliens, which in 2020 devoted an entire episode to promoting misinformation about Nan Madol. The Ancient Aliens episode misses the mark badly right from the very start. Throughout the episode, they assert that the rock moved to construct Nan Madol is estimated to weigh some 250 million tons — an assertion they repeated many times. In fact the actual estimate is 750 thousand metric tons (plus a lot of coral rubble as fill) — Ancient Aliens was wrong by a factor of over 300. Ancient alien believers are known for exaggerating, but multiplying the true number by 300 takes it to a whole new level.

(And just so you don't think I've got this wrong due to confusing metric and Imperial tons, the two are within 10% of each other. And since we're dealing with estimates anyway, exchanging one for the other doesn't make much difference for today's purposes — we're in the ballpark either way.)

Throughout the episode, they love to bandy about their favorite weasel word: "mainstream archaeology," as if working in the mainstream of a field is a poisonous, immoral thing to do; closed-minded, a slave to the status quo, refusing to accept anything outside the orthodoxy:

This place potentially is thousands of years older than what mainstream archaeology suggests.

Most archaeologists really don't want to open this pandora's box of what is there on this island because it's not easily explained by mainstream archaeology.

There is no such thing as "mainstream archaeology", any more than there is such a thing as "western medicine." There's medicine, and not medicine, no matter where in the world it's practiced; just as there is archaeology, and not archaeology. The Ancient Aliens hosts are not archaeologists; they are (by their own description) "ancient astronaut theorists". You might as well venomously spit the term "mainstream math" for clinging to the obsolete dogma that 2 + 2 = 4.

In a blatantly deceptive attempt to create the appearance of science being unable to account for Nan Madol, Ancient Aliens brought in a professor from UCLA — but were careful to bring in the wrong kind, someone who would not have any reasonable expectation of knowing anything about Nan Madol or the Pohnpeian people. They brought in Dr. Henry Burton, a professor of structural engineering, one of our top experts in building for seismic performance, and winner of the National Science Foundation's CAREER Award in 2016. Most recently Dr. Burton has been using machine learning to better assess earthquake safety — saving lives with science. Ancient Aliens hoped that he'd be stumped trying to guess at how ancient Pohnpeians moved rocks, which, predictably, he was.

So how would you build this if you didn't have any cranes?

Well I can't think of any way that you'd be able to build this... It's a mystery to me. I can't imagine how it could be built without cranes.

Why would he? Ancient megalithic techniques are not his field. There's a good reason Ancient Aliens didn't bring in someone with relevant expertise, because then they wouldn't have gotten to say:

Dr. Burton said that in order to calculate these stress levels, he would need advanced mathematics such as calculus. And that is a pretty tall order because even archaeologists would have to admit that calculus did not exist in 1100 AD.

...as if calculus is required to stack rocks. Not even the ancient Greeks had the slightest clue about calculus, and they built the exquisite Parthenon two thousand years before the basalt columns at Nan Madol were stacked. I don't remember Ancient Aliens claiming only extraterrestrials could have built the Parthenon.

Anyway, it seemed kind of mean that they picked on Dr. Burton by bringing him on the show purely as a prop to make it seem that scientists don't know anything. His pinkie toe probably knows more than the entire Ancient Aliens writing staff.

But Ancient Aliens is not the only source to spread misinformation about this fantastic site and its clever builders. Plenty of random websites and books spread it too. For example, some of the commonly-given weights of the basalt columns are way off. I read in multiple sources that the longest of them, at six meters, weighs 80 to 90 tons. That struck me as obviously far enough wrong that I did a simple calculation. Basalt weighs 2800 kg per cubic meter — almost three times heavier than water. The overwhelming majority of the columns at Nan Madol max out at about half a meter in diameter, and most are smaller. So a simple calculation tells us that the biggest such specimen, at six meters long, would weigh just over 3 1/4 tons. Most weigh substantially less.

Compare that relatively handy size and weight to the famous moai of Rapa Nui, commonly referred to as the stone heads of Easter Island. Although most of the moai average right around 14 tons, the heaviest of them weighs 85 tons — far heavier than anything at Nan Madol. And one moai that was not completed — it still remains partially connected to the quarry from where it was being excavated — would have weighed between 145 and 165 tons. Clearly the Rapa Nui had figured out moving stones to the point they were comfortable planning one of that magnitude. Their method was to use ropes to walk the great megaliths standing up, to teeter-totter them alternately one bottom corner at a time, as evidenced by the wear patterns found on their bottom corners. This method was extremely efficient, with almost no energy lost to friction as if they'd been dragged or moved on rollers. Additionally, there's virtually no practical limit to how large of a stone could be moved in this manner. That the Pohnpeians were able to move much smaller stones of a more convenient shape should be of no great surprise, and we find insufficient cause to demand an explanation as exotic as extraterrestrial stone-moving tutors.

If the basic claim of the Ancient Aliens believers is that the Pohnpeians were so much less intelligent than the Rapa Nui that they couldn't even move much smaller stones, then wouldn't a more likely explanation be that they got people from Rapa Nui to teach them, instead of aliens from some distant planet? And, when we remove the unevidenced assumption that the Pohnpeians lacked sufficient intelligence, we're left with no reason to conclude they couldn't move the rocks on their own, as was being done by their contemporaries throughout the Pacific Islands. Nan Madol is not a unique site. We find nearly identical structures on the island of Leluh, 550 kilometers to the east; and other types of megalithic works on islands throughout the region bounded by Hawaii, New Zealand, and Rapa Nui.

Consider this statement from Giorgio Tsoukalos in the context of what the Rapa Nui did:

The idea that people actually dragged these things across a rugged terrain or on rafts is absolutely preposterous in my opinion. The bottom line is that it is an impossibility to move 250 million tons of basalt from one side of the island to the other without modern technology, without modern machinery.

Maybe he's not much of an expert on ancient megalithic techniques either.

Ancient Aliens also tried to sensationalize a false claim that the source of the majority of the stones at Nan Madol can't be accounted for:

Sixty percent of the stones, they don't know where they came from.

That's incredible, that the sixty percent is essentially still a mystery.

In 2016, four years before the Ancient Aliens episode, the most authoritative paper yet was published giving the dates of the structures and the sources of the basalt — telling us that the TV writers did essentially no basic research before filming their show. Using a portable X-ray fluorescence spectrometer, the basalt can be easily petrographically and geochemically characterized, and then matched to Temwen's sources of basalt. There are three geochemically distinct types of basalt used. One comes from a volcanic plug at the Western end of the island called Pwisehn Malek; the least common come from the most recent volcanic flows called the Kupwuriso stage; and the most common stones, comprising some 76% of the samples tested, come from the main shield stage available at any of nearly a dozen sites along Temwen's northern shore. At all of these sites, weathering had naturally broken off more than enough basalt columns that workers needed simply pick them up off the ground, no quarrying required. All the basalt at Nan Madol is easily accounted for. There never was any mysterious missing sixty percent.

And finally, the age of Nan Madol. For a long time we've had a pretty good range based on the known migration patterns of people through the Pacific Islands and from carbon dating of charcoal found at levels of construction, but that's apparently not quite good enough for Ancient Aliens. They randomly threw this out there, with not even a remotely supporting explanation:

Nan Madol, for sure, had to have been built when the worldwide water levels were much, much lower. And that, according to science, was between 11 and 20 thousand years ago. So right there, we have physical evidence of a site that, in my opinion, was built in prehistory.

Well, Uranium-Thorium dating doesn't lie, and its results were widely available to the Ancient Aliens writers if they'd wanted them. The cleanest, newest coral used in the tombs for the first Saudeleur kings were in place no earlier than 1180-1200 CE, and construction of similar monuments on other islands in the region commenced 1300-1600 CE. Spanish and Portuguese explorers were already plying these waters, and none reported flying alien construction cranes.

Ancient Aliens did almost get one thing accidentally right, though. The sea level was indeed lower when Nan Madol was built — just not by nearly so much as Ice Age levels. Volcanic islands are very heavy, to the point that they actually press down on the oceanic crust and, by their own weight alone, slowly sink. Pohnpei has subsided some 4.3 meters over the past 5,700 years, as evidenced by carbon dating of materials found in ancient mangrove sediments. At the time of Nan Madol's construction, sea level at the site was approximately 1 meter lower. While the canals between the artificial islets are awash during normal tides today, at the time of their construction they were high and dry. Although islets today, they were simply platform structures at the time. This is an error you see repeated in nearly every pseudoarcheology blog or article about Nan Madol: they refer to it as a port with canals, and compare it to Venice. Nope. It's only that today because the island has sunk since it was built and used by the people who simply walked around atop the coral between the platform structures.

And so I conclude with an epistle that you please not give any oxygen to fake history or fake archaeology shows like this one. They're wrong, and they attempt to de-educate the public because it's so easy to just make up sensational nonsense to get clicks and views. Conspiracy theory culture and anti-intellectualism are thriving well enough on their own without us helping them any.

Correction: An earlier version of this made references to the islands of the South Pacific; Pohnpei and Temwen are actually just north of the equator. —BD

By Brian Dunning
Follow @BrianDunning