@Judi, since “tightly-fit-together stones” seems to be your only basis for concluding that a structure was built by aliens, could you elaborate on which specific structures—or specific parts of structures—were built by aliens?
Obviously some pyramids and zigurrats are better-made than others. How many did the aliens build? In lieu of the less visible sloppy stonework on even fancy pyramids, is it possible that the aliens only carved the outer stones but outsourced the inner stones to humans, or perhaps less competent stonecutter aliens?
I’m also curious as to why aliens with technology to travel light-years across interstellar space bothered to build… well, the second-most basic building structure in human civilization, a “big ol’ mound of stones.”
“Space Emperor Zargon, we are orbiting earth. The primitive ape-men have evolved the ability to make simple, hill-shaped buildings out of earth and cut stone. What should we do?”
“Build one of those things! Yeah!”
“Okay. How big?”
“Slightly bigger than the biggest one the humans have built!”
“At your command. Should we make it hover in mid-air or function as a supercomputer or…”
“No, just do a fairly precise job cutting and joining the stones. We don’t want humans to get the impression that spacefaring aliens made this thing, you know!”