A lot of things are possible when you have a population that is deeply socialized to believe completely in the cause, and/or has few viable economic options, and/or is literally compelled to do the work. We also have a lot of survivorship bias as the we only see the stuff that was done so well as to stand the test of time. In the early days of Egyptology for example, they would sometimes realize (or learn from the locals because the locals knew best) that the big heap of rubble over there in the desert was actually a pyramid where somebody half-assed it with mud bricks instead of the giant limestone slabs from Giza.