In my humble opinion, scale modeling is the only way the Incas could have built such extraordinary architecture utilizing in some cases monstrously huge boulders and/or giant pieces of quarried rock which they shaped with multiple and irregular sides and then formed with mortarless joints into many awesomely dramatic walls found in places like Cusco, Machu Picchu and others.

This appears to be a unique position as I have never seen or read anything by anyone else that champions this thought. But I reckon it’s the most plausible. And the technology of ‘scale’ is quite probably pre-Euclid; meaning that the awareness of scale in geometry existed maybe 2 millennia before the Incas came on the historical scene.

The other methodologies that have been hypothesized thus far [to me] make less sense. Repeated lifts, tracing the shapes, shaping the stones in mid-air, and/or utilizing templates; all prove in the short analysis to be neither comprehensive or complete .

I am not interested in dissuading anyone of these hypotheses although I must say that repeated lifts is absurd – just stand in the ruins of Sacsawaman if you want to see what I mean. And neither tracings or templates can address the changing shape of the stone in the x-axis direction as one proceeds deeper into the joint.

I walked the Inca Trail in 1999 and then again in 2000 during which I also spent a fair amount of time in both Cusco and the Sacred Valley. As an engineer I didn’t see the ruins so much as I did the mechanical aspects of the architecture; continually pondering over the building techniques.

After wandering around Sacsawaman for the third or forth time I eventually came to the conclusion that the designers must have used architectural scale models to both design and build their monuments. It was in my opinion the most viable methodology in light of enormity of some of the pieces. It’s like with chimneys; after it’s built and sticking up through your house – there is no delete function. And it only stands to reason that the builders didn’t want to have to move those mammoth pieces of stone anymore times than they absolutely had to. And it also stands to reason that the weight/size/(un)moveability quotient would be right at the top of the design criteria list. I know it would be mine. And the Incas certainly wouldn’t/couldn’t have trial and error those mega-ton stones into place; not with those highly precise fits – which was another top priority line item on the same design criteria list. And you knew in your mind – that is if you put yourself in the place of the builder – that you wouldn’t want to try to lift some of those pieces into place but one time and one time only.

Back in Texas in the early part of my career I worked in the oil/gas/petro-chemical industries. This was the late ‘70s and early ‘80s when drafting was still done by hand. Many large petrochemical plants and/or their additions called ‘units’ were first modeled to scale. For example, in 1983 we built a $130M Chloroform Unit in Ingleside, Texas for DuPont Corp. But before it was built, ‘modelers’ created a – I don’t know specifically (it’s been so many years) – something like a 1 / 32 scale model of that unit representing every last fitting and pipe run. The scale of the model in other words was 1/32th of an inch equals 1 foot. That model like all other models were precise and all inclusive and in some cases cost a quarter of a million dollars or more. But that cost was justified in that when the construction and fabrication drawings were prepared that they’d be 99% correct. This meant that the pre-fabricated pipe and whatnot would fit the first time and that there would be correspondingly little field rework, which is/was very costly.

It’s not an oversimplification to see that those modern models of industrial plants were nothing more than a collection of 3-dimensional shapes  – just like the Incas stones; everything stretches out in the X-Y-Z dimensions. So applying this modeling concept it seemed very reasonable to me that the Inca architects did the same. First they chose a site, produced a design, roughed out their perimeters, laid their quarried stones around that perimeter then chose some particular stone as their alpha stone which they then shaped first. After which they built a corresponding model of that alpha stone to scale. The remaining quarried stones were concurrently pre-dressed based upon their respective shapes. The architect counted and evaluated the pieces as they related to his greater design and then set about to model their shapes and joints. I would have imagined that the architect had both a master model set and corresponding model pieces that were distributed to each rock-shaping team. Those toy size scale pieces were then used to cut and fit the big stones to their necessary size and shape. If there was a design or work order change then the change was first applied to the model.

Maybe you might have had to have seen a room size scale model of an enormous petro-chemical plant to have had a similar epiphany but to me it seems entirely logical that this would have been the method employed by the Incas to produce such perfect fitting masonry. They certainly had the engineering and math skills to have built models. And you don’t have to be a genius to figure out that making mistakes on a smaller model of something is infinitely more desirable than screwing up a 50 ton piece of rock that already cost your project many man-weeks of labor in quarry and transport time.

Just a thought…