The Enigmatic Circles of Moray



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Readers of this blog must have wondered where I disappeared to over the last two weeks. Indeed, I was away – traveling in South America (Peru and Chile). I went to Santiago to attend a workshop on modeling innovations, but most of the time I spent in Peru. Together with two friends we toured Cuzco, the Sacred Valley of the Incas, Machu Picchu, Moche, and Chan Chan. This was a remarkable experience. I learned a lot about the Andean civilizations, with which I had little previous experience, and, I expect, I’ve collected much fodder for future blogs.

When traveling to Inca and lowland sites, we generally avoided hiring guides. The problem with guides is that if you see anything puzzling, they always come up with a ready explanation. And you never know whether they just made it up, or whether they are repeating a bit of received wisdom, which has long been rejected by professional archaeologists.

As an example, one of the first – and spectacular – Inca sites we went to upon arriving on the Altiplano was Moray near the town of Maras. This site has three very unusual structures. They look like inverted step pyramids:


(photograph by P. Turchin)

Instead of steps leading up toward sky, as is the case with the usual ziggurats, in Moray giant steps descend down towards the center of the Earth. As we were driving up to Moray, our driver said: “This was an Inca agricultural station!” I have already heard this theory, of course. Perhaps the most lurid version is given by Wikitravel:

The Agricultural Laboratory of the Incas – Three large natural depressions in which terraced co-centric circles were constructed. Seeds cultivated at this site were likely sent throughout the Incan empire to improve yield in the harsh conditions of the Andes and were probably one of the benefits offered by the Incas for peaceful incorporation of neighboring tribes into the Incan empire. Today the site is a series of co-centric circles on plateaus 400 m above the valley floor (3,200-3,500 m above sea level). The site was designed by the Incas to take advantage of natural depressions below the level plain and model Andean, jungle and semi-tropical environments for the growth of different plant varieties. Pollen studies indicate that soils from each of these regions was imported by the Incas to each of the large circular basins. In the largest of the depressions (150 m) a series of water channels can be seen finding their way to the bottom. Studies have found temperature variations up to 5 degrees Celsius.


A smaller circle of Moray, showing what they looked like before being restored (photo by P. Turchin)

Only a person completely innocent of any feeling for history could write this passage. Folks, a systematic pursuit of knowledge using empirical methods is a very, very recent invention. Agricultural science started in Northwestern Europe in the nineteenth century. When Spaniards conquered the Inca Empire they came from a society that had very little modern science, and certainly was innocent of the notion that you could scientifically develop crop varieties.

It boggles the mind that the Incas, whose level of development was roughly equivalent to the Egyptian Old Kingdom, or Shang China, would do the things described so glibly in the Wikitravel paragraph above. If you want to make such a claim you need very strong evidence.

And what is the evidence? That different terraces could vary in temperature by as much as 5 degrees C.

In my previous life I did research at several agricultural stations and they typically have very utilitarian architecture and landscaping. Nothing as elaborate, precise, and beautiful as the Moray circles. If I wanted to do agricultural research in the Andes, I wouldn’t dream of investing a huge amount of labor into constructing these beautiful cones. Instead, I would take advantage of natural variation in elevation and sunlight exposure found on any decent Andean slope, like this one.


(photo by P. Turchin)

Terence D’Altroy in The Incas (which I carried with me throughout my Andean travels) comes to the conclusion that agricultural experimentation is an unlikely explanation of the Moray circles.

So what is the explanation? Well, I am not a guide whom you have hired for 20 soles, so I am not required to tell you anything.

The best answer is that we don’t know. D’Altroy suggests that, most likely, the Moray structures had some kind of ritualistic or symbolic function. Yes, ‘ritual’ seems to be the default answer for almost anything, for which we don’t have a ‘real’ explanation. It may be a facile answer, but generally speaking any beautiful nonutilitarian structures, in whose construction a lot of labor was invested, have a ritual or symbolic purpose. So it’s as good an answer as any.

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Chris Kavanagh

This might reflect my naïvety but if different crops were cultivated on the different steps might there not be a way of detecting it in the soil? Maybe it’s not a topic that has received the level of attention necessary to motivate such efforts.

Peter Turchin

But even if this was true (different crops cultivated on different levels), it’s consistent with either the agricultural experimentation hypothesis, or rituals. The Incas grew several crops for ritual purposes, most notably, coca and maiz. (Both were also used as a narcotic and a food, respectively).


The architects and artisans of Moray created a beautiful space for people to (maybe) sing (how are the acoustics?), play, and be together in specific ways that are unknowable, but the elegant architectonics seems to argue for artistic and non-utilitarian uses.


It seems that’s a theatre.

Ross David H

Yeah the first thing I thought when I saw it was, “everybody sitting or standing on all of those terraces can all see the thing in the center”. Which is a structure known to be used in many different societies over the course of millenia. Not proof, of course, but it seems a simpler explanation.

Gene Anderson

Looks like a theatre–very similar to Greek and Roman theatres. Probably for ceremonies. But, Peter, you really can’t say that “systematic pursuit of knowledge using empirical methods is a very, very recent invention.” I’m not sure what you’re doing with Aristotle and his many followers. And in fact all traditional societies know perfectly well how to evaluate crops and cropping practices, and figure out good hunting procedures, and so on. If you want formal methods, the Chinese were reporting on systematic case/control experiments in agriculture, on government agricultural experiment stations, by around 120 BCE (in Fan Shengzhi Shu, an ag extension manual of the time). There is plenty of Chinese science since then–see Joseph Needham’s huge series SCIENCE AND CIVILISATION IN CHINA. The extent of Inca technology seems to make it clear they had some sort of systematic way of evaluating empirical knowledge.

Peter Turchin

Chinese did it first? Again? OK, thanks for correcting me, Gene. But I will differ with you on Aristotle. The Greeks valued philosophy and theoretical knowledge, but were fairly disdainful of practical knowledge and I am pretty sure they had no idea of controlled experimentation.

Still, I believe my larger point stands. The Moray circles are too beautiful, and too much work was invested in them, for them to be purely utilitarian structures.


Driving in the hinterlands of the Peruvian Altiplano near Lake Titicaca in the early 1980s I saw a large circular pit much like your pictures. It was next to an agricultural village and was being used to grow crops. I have hunted for documentation on this system but with modest success. Clark Erickson, who studied raised fields on the margins of Lake Titicaca, has a diagrammatic drawing of conical sunken fields as one of several landscape management techniques used in the Altiplano for agricultural purposes. He provides no commentary on them however. My guess at the time was that with the tropical sun nearly overhead even in the cold season that protected pits would warm considerably during the day and radiate infared at night, creating a frost protected microcosm for growing crops. At elevations of 3800 m + frost can damage potatoes and other crops in almost any month of the growing season. Of course, such a pit would also make a comfortable place for spectators to view a ritual for the same reason!

I would think a theater would likely be situated in or near a city with elite architecture and a sunken agricultural field near a rural village. But I suppose a sunken field might be the kitchen garden of a cook for the elite, and a village sunken field might be dual purpose.

Clark L Erickson. 2006. Intensification, political economy, and the farming community. In Agricultural Strategies, Ed J. Marcus and C. Standish. Cotsen Inst., Los Angeles.

Peter Turchin

This is a very interesting observation, Pete. A difference of 5 degrees C between top and bottom is very significant, and would yield a lot of protection for plants growing in the bottom. What did those circular pits look like? Were they similarly meticulously arranged?

It’s quite possible that the pits started as devices for creating microclimates favorable for growing plants under adverse conditions, and then evolved to have a ritualistic function. D’Altroy speculates that Moray circles might have been part of a royal clan estate. Most of the Inca ruins we see today (Machu Picchu, Ollantaytambo, Pisac, etc) were the estates belonging to royal clans. They had multiple purposes: residences for the elites, military installations, and ritual spaces. So Moray circles may have had multiple functions, also.

Peter Turchin

On the acoustics of the Moray circles, here’s what one of my travel companions reports:

“Yes, the acoustics were very good, with no echo and decent projection. As a choral singer I judge it could very well have served as an amphitheater. What we didn’t do was have me go ‘on stage’ and try having you guys at different levels to see how quiet I could be. A missed experiment, damn it!”


I am with you. The folks who think this is an agricultural tool need to get out there and do a little more work with a pick and shovel; or better yet their stone age equivalents.

This has “important social function” written all over it. If it is an amphitheater, it is laid out oddly. But there does seem to be some sort of schematic ordering to its varying levels.

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