Inventing the wheel.

I was reading about Machu Picchu and Inca stonework last week, and came across the hoary old colonialist talking point that the Incas did not invent the wheel. Being in a "go down internet rabbit holes" mood, I found myself reading various explanations for why precolumbian Americans, despite having wheeled figurines (see: image here and writeup here and early prototype pottery wheels (the kabal/molde, never scaled those figurines up or broadened their application to transport. Very few of the explanations sat well with me.

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Central American pottery wheels were still at the "spin the pot relatively slowly while laying coil" stage when the Spanish arrived. Not all the pieces had come together yet, and thanks to the conquest, they never would.

(extra bits that I found while writing this but that didn't fit are in comments)

Incas and masonry

Famously, the Incas did not use mortar in assembling their stone buildings, which were so perfectly carved and set that there was essentially no gap between the blocks. Each hand-carved stone block was made to mirror the concavities of the block below with convexities of its own, so that once laid, the blocks interlocked, with each course resting in hollows in the course below - this made the walls extremely durable in the face of earthquakes. The stone masons took irregular rocks and made them fit together perfectly without doing away with the irregular shapes, resulting in striking patterns in the stone. (OTOH, they also made walls with rectilinear blocks; I think the thing was they used whatever rock was at hand. Loose rocks cleared from the construction site produced irregular shaped blocks, while quarried stone produced rectilinear blocks)

The outside faces of the walls were chiselled and sanded smooth for aesthetics, especially on more important buildings and high status homes. The inside faces were usually not cut or polished smooth, and there was not as much care to make the gaps between blocks as tiny as possible, except in the very highest status buildings.

But, I had trouble finding imagery that contrasted the pretty vs not so pretty sides of a stone wall, so I'm not sure just how much the inside walls were different from the outside walls. Decorative bas relief carvings were sometimes executed on the blocks. The Incan stonemasons were willing to work with whatever sized rocks were handy, from small blocks to megalithic scale boulders.

Looking for information about Incan stonework led me to a fascinating article that tries to untangle just what it was that the Incas used instead of mortar. We know from early Spanish accounts that they did use something, which Spanish eyewitness chroniclers did not properly understand but tried to describe anyway. Some said the Inca stone workers used a reddish mud. Others, that they poured molten gold and silver into the cracks between the stones. The Incas themselves said the stones were made to flow into place. The article assembles all these tidbits and suggests that the stonemasons were using mud from copper and tin mine tailings, in which sulfer-metabolizing bacteria would eat iron pyrite, producing extremely strong sulphuric acid. Chemical reactions between the acidic mud and the rocks would have given off steam, and that plus the glitter of fool's gold might have confused the chroniclers who wrote about molten metal. Acidic mud, the author argues, helped to temporarily soften the stone of the blocks, encouraging a more perfect, gap-free fit as the softened stone would flow ever so slightly as it re-hardened. Close examination of the joins between stones today shows a tiny discolouration that suggests such a chemical reaction took place. It's fascinating, and worth a read if you have the time. Otherwise, enjoy photos of incan masonry here.