I recall reading, I believe in Scientific American, some time in the mid eighties, a report of some replication experiments done with inca stonework to answer basically the question of how they got such precise fits, straight lines, etc. Certainly, there have been claims that they couldn't possibly have built their drystone walls to such precise fits without the help of advanced civilizations, but as usual we underestimate the ingenuity of our ancestors. I'll see if I can find the specific article, but I'm going to post a brief summary from memory. I should also add that I've tried this, and it works.
First, hard stones aren't carved with chisels. Chisels are for marble, soapstone, sandstone, and such. When you use chisels on hard stone, the edge of the chisel blunts or breaks. Harder stones are carved by impact. The modern tool is a bush hammer, which has lots of little points to crush and spall rock away from the impact point. It looks a lot like a meat tenderizer hammer, but with a hardened steel face. The primitive tool is a cobblestone of a rock at least as hard, but ideally harder than the one you wish to shape. It can either be a hand held cobble, or one with a handle made by wrapping a split of flexible wood around it and tying it in place.
The incas planned ahead a bit when quarrying their stones, and left knobs on them to attach ropes and allow easy handling. Stones with the handling knobs fractured off have been found abandoned on the roads leading from the quarries, suggesting that the presence of the knobs was important. Stone walls have been found with the handling knobs still intact on the outer face, or with marks where the knobs were broken free after the wall was built.
The technique the researchers found most productive in making straight, tight joints between stones was to dust the bottom stone with stone dust, and lower the top stone into place. Its weight would compress the stone dust and leave a clear impression of where stone needed to be removed. Impact spalling with a hard cobble would quickly break the stone away from the places it needed to be reduced in size. The most daunting task was the several times that the top stone had to be lowered into the course before it was sufficiently well fit to be left in place, but it was manageable using brute force, ropes, and levers.
No advanced technical help needed, just a good understanding of how stone is worked combined with plentiful labor.
A.
I found a reference that I'm about 99 percent sure is the piece I remember reading. Its Protzen, Jean-Pierre; "Inca Stonemasonry," Scientific American, 254:94, February 1986. I can't access it directly to see, since its a pay site, and I no longer collect magazines to the obsessive extend I once did, so I'm unable to confirm. (I once had a complete set of scientific american, colliers, and national geographic. It took up a fair chunk of my library. It's amazing what libraries get rid of, and how cheaply. I read them end to end a couple of times, then gave them away.)
