Cusco, Peru

The existing theory to explain the precision of these joints is that each block was painstakingly chiselled and re-chiselled to fit the irregular, often multi-faceted profile - but no chisel marks are found in the joints that have been exposed by seismic activity or repairs.

Applied heat is an unlikely explanation due to the absence of vitrification (and the vast amounts of energy that would be needed), chemical stone softening – if possible – also permanently alters the crystalline structure of the rock and any theories involving ancient power tools have the same problem: What was the ancient power source?

According to a geologist colleague, this stone (andesite in many cases) is simply quarried - but it appears as though the workers just piled up these blocks like big lumps of marshmallow.
As strange as it may sound, it appears as if the stone were somehow softer at the time.