Sacsayhuaman. The technology used to shape those natural hard limestone rocks is still unknown. At least they had to soften the stones to create those perfect jointless fittings without mortar. Other possibility: Nature provided plasticine like shapable stone for a short time span. The hidden contact surfaces between the stones within the wall are mostly perfect fits without any filling or space in between. You find the exact same construction technology in the oldest Egyptian temples like in Giza and Abydos. That's different to Greek or Roman mortarless walls where the hidden stones surfaces are of concave shape with only the edges touching (anathyrosis).