Ancient Alien Architects of the Gods Department (originally from Mysteries of the Multiverse)
Have you ever wondered why the space aliens taught the ancient Egyptians and Incas how to cut and move 100 ton blocks of granite, but never bothered to teach them how to build anything but primitive post and lintel construction? No domes, arches, vaults, buttresses, cantilevers, no concrete, no metal reinforcements, no internal frameworks?
I guess there are some things MAN WAS NEVER MEANT TO KNOW.