A geo chemist has shown that the pyramid stones are a geopolymer (not concrete but similiar) so actually they are mush when poured and o of course make tight fits with surrounding stones.

Brain Forester (great youtube videos) has a great shot of the BACK of one of the walls machu pichu and you can see the bsck of the stones are giant boulders and its onoy the front that look like the wall which is strange.

Also the old south american builders used concetrating gold hand parabolic mirrors to light fire so they knew how to concentrate sunlight for heat. Some old texts say they used giant parabolic gold mirrors on nearby mountains to reflect heating sunbeams on the rock faces to soften the stones so they flowed together tight. Surprisingly it doesnt take as much energy as you might think to soften stone to it will sag (not melt but just turn putty like)

Google "geopolymer pyramid"

And "gold mirrors to melt stone"

You only need 2 square meters of su light to melt anything on earth in one second or less. See this proof. https://m.youtube.com/watch?v=z0_nuvPKIi8 So of you had a larger mirror focused for a long period of time you could slowly soften a large area of rock bit by bit to make the edges sag together one by one. And remember on the back these big stones are just regular boulders. So its onpy the fronts that are tight together just as if the fronts were soften by mirrors. Needless to say everything gold was stolen so those big "discs" as the spaniards called them wheretaken away.