Saw a documentary years ago hypothesizing that the Inca made the mortarless joints by throwing down a hard, spheroid rock atop the block they were shaping. It was thrown down with a back spin, what we'd call "English" in pool. ... Is that what the tour guides are sayin' these days? Or did they even get into that?
I don’t recall them explaining the process. But with the deluge of info you get on a tour, it’s possible.
I took a quick search on YouTube, but they were mostly far-fetched theories cooked up in basements. Could be some good ideas are out there, but I wasn't up to wading through the BS.