Some say Extra-Terrestrial's have been "our" guidance for constructing monuments in their honor, I say Bologna, Hogwash, Balderdash, Malarkey, Ox Droppings. Quit Pulling my leg and stop, halt and fully realize before I am done that the "Ancient Alien" theorists are "spewing" nothing more than Cow "patties"
The truth in History is more than likely in what has been buried or diverted from thought rather than what has been preserved "loudly". The word "Alien" is defined as one whom originates elsewhere, that covers just about all of us. The 2nd most perplexing question ever asked is "Are we alone" in the Universe? This question is still asked today, therefore it is not quite answered, as of yet!
Humanity carries a duality, it runs deeper than most people can comprehend. The "ancient Greek" mythos provided a clue to this when it describes the division that caused the creation of "Man" and "Woman". We are forced to be forever searching for our "other" half and that is a "Duat".
This philosophy actually originates from whom the ancient Greeks regard as their ancients. This reclusive Race of "beings" had tools and machinery far more advanced than any other and could construct structures to survive the centuries. Thier mathematical specifications even baffle engineers to this day, hence why "Ancient Alien" theorists know very little to nothing about what they are trying to say.
Ptolemy proved through mathematical equations that in the "Tera-centric" sky, the planets and stars spiral around themselves while striding across the "Heavens". But why blame "him" for thinking that, As there is as much of the Universe to "your right" as there is to "your left". It was merely prospective of a perspective, what "he" lacked is an outside perspective. Mainstream society has been told one thing, but I have learned another. For example, an Orca has been called a killer "whale" and a Koala has been referred to as a "bear". On top of all that, rarely can a story survive a line of 10 people, let alone when you try telling a story to a million people with different tongues across 5,000 years to those whom speak different languages. You get people who think the Latin meaning for "flying chariot" translates into "hovering craft".
I would be incredibly ignorant to believe Earth has the only life in the Universe. To believe "we" Humans are the only intelligent or capable beings in this galaxy is even more ignorant. I would even have to admit the very real possibility of "alien visitors". But several undeniable facts stand firmly against an "extra" terrestrial influence on our ancestors.
First, every one of the supposed alien monuments are constructed using a Humans perspective. Second, If there was a Race of beings capable of ">C velocity", they would want little to nothing from "early" Humans. Third, having us to worship and idolize them, they would have "set up shop" and never would have left. In other words, they would have had to wipe us out or conquer us, that didn't happen. Forth, If they did try to help or conquer us, it is quite unlikely they would have survived the "common cold" or we would not have survived their common sicknesses. Fifth and the most damning evidence can be the fact we don't treat our own "kind" well, so another being so different than us would not have been treated any better!
I find all "ancient alien" theories offensive due to the mere fact that they put so very little faith in Humanity and it's true reasoning is "IN MY OPINION" sort of racist. When you consider ants developed Heat Ventilation and Air Conditioning more than 500 million years ago and did that through chemical communication, you realize how very much "our" abilities are underestimated or how some think Technological Advancement never suffered a regress.
Instead of believing "little green men" did it, consider that a "brown" skin with a "brain" could have done it with what seems to be grossly absent from "modern man", workmanship.