I think, the further back in history we go, the kookier things get - and that this is a positive, not a negative aspect of the experience. We in the modern age have conditioned ourselves to be subjugated to science - well, for the humans alive 20,000 years ago, cave-paintings were science. The fact that we don't understand them now, and have very strong opinions about the nature of civilisation in that period of human history, is more of the effect that time and history have on human consciousness - namely, occlusion and obfuscation. Kooky explanations for the weird and unusual artefacts we discover in the modern age are to be expected - we are as oblivious to the meaning of ancient art/science as they would be, had we a time machine, of our modern rocketry and iPhones and so on.

I think the Imperial View which tends to lead one to discount observations made beyond the lunatic fringe is less valuable than the conjecture and supposition that occurs when someone, perhaps weird and unintelligent, says to themselves "What if ...?" and then subsequently go off to investigate.

Never forget, even Newton was considered a crackpot for a period. We kill and eat our messiahs, after all, it is an ancient and provocative segment of human psyche, that we have been unable to shake the bonds of cannibalistic behaviour in our societies - sure, we're not cooking and roasting on an open fire, unless that fire is a metaphor for the modern thinker, convinced of their own righteousness.

I'm personally unconvinced that there weren't ancient civilisations with advanced technologies, yet undiscovered, which moved mountains for their own purposes.

We need only look at the deleterious effect of technology in our own generation to understand just how banal things can get, vis a vis forgotten science, and specifically technology. Perhaps the ancients did have anti-gravity capable flying machines that allowed them to build these structures - and perhaps the tech was lost in a few generations because of the deleterious effects of "planned obsolescence" at such scale. Unless someone is willing to stick their neck out and ask "What if .. there are UFO's buried under these mountains/&etc.?", we'll never really know.

Of course I understand the requirement that sense trump fiction - however I don't agree that the line is so drawn in the sands and stones of the ancients. There are many, many signs that we do not understand, and yet many clues that there is more to ancient history, and particularly civilizations beyond our comprehension, than there is 'total certainty of fact'.

Heck, even the Pentagon admits it doesn't know it all about UFO's, c'mon ..