most ancient civilizations credit beings from the sky for the knowledge they where given....this is a fact.
but do we have to take this literally? To mean that extra-terrestrial beings travelled to Earth and physically built structures for different civilizations at different times around the ancient world. IMO the sky is more of a symbol for the spirits and universal knowledge that some of the civilizations before us were more in tune with than we are today. They looked to the sky like we still do, but had a different way of expressing and explaining it.