Some of the walls were built on very steep mountain ridges and I think it is involved with some architectural principles to make the wall balance; also, from the aspect of construction material, they have followed the principle of using local materials, that's why walls on moutain ridges were built of stones, walls on plains were built of rammed earth or bricks, and walls on desert were built of sanded reeds and juniper tamarisks.

i think so to