Geopolymer or Natural Rocks? The Geological Truth of Sacsayhuaman, Peru | Ancient Architects

Situated next to Cusco in the Inca heartland of Peru, Sacsayhuaman is one of the most incredible ancient structures in the world. It’s truly mind-boggling how such enormous blocks of stones can be so randomly shaped yet so perfectly put together. The origins of the megalithic blocks of Sacsayhuaman, Peru, have long been a source of debate because it really feels like a genuine mystery.

These are large blocks of limestone, sometimes huge, most of which seem to pillow or bulge out instead of having straight, sharp cut faces. Some blocks seem to curve around corners, others have scoop marks on the surface and a number have the famous nubs. There are many other seemingly bizarre and unnatural features. Each block is irregular and each is unique yet the joints between these limestone blocks are perfect. So how is this even possible?

I’ve speculated in the past that maybe some kind of stone softening agent was applied, possibly some kind of acid. At the end of the day, we can stare at pictures and speculate forever; what we have to do is look at the science. I’ve always said that samples need to be taken and the geology needs to be analysed and that will tell us everything we need to know about Sacsayhuaman.

Well, little did I know that such investigative work was done back in 2012 and in this study and take a detailed look at the geology of the blocks of Sacsayhuaman and so, once and for all, we should be able to answer the question - are they artificial geopolymer or natural rocks? This video is the geological truth of Sacsayhuaman.

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[AncientArchitects]

Thanks for being here and watching! I made this video whilst having a very bad cold, and hence the audio quality is lower than usual. I even lost my voice twice whilst recording and also had to give the video a couple of re-writes on finding new information over the past 7 days. I know this video is very detailed but I thought for this subject it would be best to be as thorough as possible! Thanks again and enjoy!

[datra]

PhD Geologist here with extensive experience in petrography. I have been to Sacsayhuman several times and, while marveling at the mysterious construction, agree that the blocks are not cast. Here is my reasoning.
1) Many of the largest and lowest blocks are composed of breccia and are fairly porous, unlike the upper blocks. If they were cast, why would they include such large fragments and (relatively) high porosity? They look like reef talus breccia to me.

2) The smooth mating surfaces are striated and limited to the outer few inches of the contact areas; the inner areas of the contact surfaces of both the upper and lower blocks are usually slightly concave, which is an excellent design for achieving a tight fit. If the blocks were cast in place, there would be no concavity on the mating surfaces, and the surfaces would not be straiated (an effect of grinding).

3) The uppermost and smaller blocks are indeed composed of micrite. Nevertheless, they contain intact crinoid, gastropod, finestrella, and brachiopod fossil fragments which would never have survived the crushing and grinding needed to make castable paste mix.

4) The chemical analysis correlates between a sample from the quarry and one of the blocks (need larger data set). This is not surprising were the block removed from the quarry. However, I suspect that the high heat needed to make castable lime would change the chemistry, especially that of the oxides. This could be tested by taking a quarry sample, analyzing its chemistry, preparing the burnt lime, then re-analyzing.

I certainly don't claim to understand how the blocks and walls were made, but science is mainly a process of eliminating the untenable hypotheses. In this case, I think the evidence that the blocks were not composed of man-made, cast-in-place cement is undeniable.

[efbjmlk]

Ancient architects way of combining an open mind with peer-reviewed research is unbeatable. Many thanks for the time and effort you put into your videos :)

[insertphrasehere]

Another fellow geologist here (engineering geologist actually).
The reason why the blocks are shaped in such a way as to 'bulge out' is because this allows them to avoid sharp right angles on the edge of blocks. Sharp angles that come to a 90 degree 'sharp' point are very vulnerable to stress, and to weathering, and result in chipping that breaks the edges of the block. Especially with unmortared blocks this gives the profile of the corner a rounded angle, but still allows the blocks to come together with very sharp boundary.
If you made these blocks square, the edges would be much more prone to chip, showing gaps and spoiling the effect.

[justthatbloke]

When I was studying for my architecture Masters, I found a book in the library which talked about dozens of small, angular-shaped stones that were discovered during the excavation of Sacsayhuaman. At first, they thought that they were children’s toys based on the architecture (e.g. like a doll’s house), but then they realised that the stones fitted together perfectly. After collecting up numerous stones, they found they could make exact, precise models of parts of the walls - all the angles and surfaces were correct, scale versions of the finished wall.

Not sure if this has been commented before, but I can’t find anything online, or remember the title of the book.

[klubstompers]

"How have we not found tools in the work sites?" I dont leave my tools on the job site when im done, i take them home. I dont know anyone who does. Tools are expensive, especially if they are made out of rare and hard to come by, and hard to forge, metal. Any piece of it would be recycled back into another tool, and closely looked after.

[williamchamberlain]

3:15 now _that_ is a bad argument.
1) If a block were bulging out from it's own mass or the mass above, each outer and inner _face_ would also slump under its own mass, not protrude symmetrically top and bottom.
2) If a block were bulging out from it's own mass or the mass above, why would the bulge be symmetrical on the side edges?

[davids]

Ok, i just have to say... no matter which way you slice it, (no pun intended 😛) a process that is unknown to us that has happened here. Isnt that still "ancient lost technology" doesnt matter if its machinery, electric or chemical its still technology isnt it

[Rastafarai]

I have located a similar site in Southern California, on private property. This is a site exhibiting the clear signs of pre-Inca (Caral-Supe?) tight clearance rockwork. The site was buried, and was exposed after a fire caused the dirt to fall off the hillside. I have videos and pictures of the rockwork which was exposed beneath a massive 500+ year old paddle cactus. There is a formal catwalk beneath the landslide area and I assume that someone began excavating this area at some point, possibly in the 1970s. The site is in the back of a residential home on a large private avocado ranch outside Carpinteria in Santa Barbara County. I am looking for some official backing, so that we can approach the property owners with a proposal to investigate.

[justjoe]

I feel that the thing about all of these ancient stoneworks is not just how they did it... But that they knew how to do it.

[atticuspaine]

You talk about the job being too large to be possible. But what you don't understand is the job that it would be to carve those stones to fit as tightly as they do in such a symmetrical positions. As a stone Carver I can assure you the difficulty of doing that would equal any difficulty of creating the stones from a clay-like material.

[stargate]

Your videos are so interesting. You have a "here's what I know and why I know it" approach and that is praiseworthy. I've also seen you correct yourself with followup videos upon further investigation and updating your previous hypothesis. Rarely does anybody else do that. Thank you for your hard work.

[JonnoPlays]

This was amazing to watch. It's so strange that the science on this topic is so undiscovered and undiscussed when it's really the greatest mystery we could solve.

[TheDeadRabbit]

Keep it up brother! You have no idea how important this information is to people's minds. Keep it going! We're here for you.

[RostislavLapshin]

Several methods of fabrication of the polygonal masonry using clay/gypsum replicas, a topography translator, reduced clay models of the stone blocks, and a 3D-pantograph are described in the article “Fabrication methods of the polygonal masonry of large tightly fitted stone blocks with curved surface interfaces in megalithic structures of Peru” (DOI: I do not provide a direct link, because YouTube does not allow a comment with this link. Search by the article title.

[remkoburger]

Apart from my appreciation for Matt's hard work, I also want to pay my respects to Google Translate. It really opens up whole new worlds.

[gregsmith]

"Working them together?" You don't know how hard this is. It's unbelievable.

[jamesshoffner]

I lived in Peru for 25 years. I have photos of rocks that were obviously poured into a mold. In Cusco, there is a large corner stone that was struck by a truck while it was backing up. The 3" rendering that covered the rock, cracked and fell off after being struck by the truck. What was left were all the stone behind the rendering that were used to initially make up the body of the wall. After seeing that, it all made sense to me now the walls were so perfectly made.

[anthonyhudson]

I used to have a business casting concrete products, and when I first looked at the site I wondered if they were cast. The bulging being a big clue. After listening to Matt however, I am now wondering if the big stones were cut and the smaller ‘fill in’ blocks were cast. It does not necessarily have to be one thing of another. They may have used a variety of construction methods.

[stevewhitson]

My education and work was in Geology also. I have been fascinated by these incredible blocks for years. You presented the first intelligent info on how these rocks may have been made. The mineralogy doesn’t lie. Thanks so much.