I'm not sure if it was aliens or not, but certain things are virtually unexplainable. Like some of the stone carvings at acute right angles that even laser precision couldn't duplicate even in modern times. Gigantic statues made of solid rock, carved perfectly, that even today's best heavy machinery would have issues moving, and on top of that? It was mined and transported from hundreds of miles away.
I'd like to think that aliens would be far superior to us as a whole on the intelligence level, so I doubt that is the explanation. However I do wonder if the civilizations that we perceive to be primitive to what we figure them to be were in fact much more intelligent than we give them credit for being.
Shit (history) gets lost in time. Maybe it wasn't important to them for one reason or another to continue the knowledge. Maybe they figured it would be commonplace that people would pass it down... but they didn't.
People like to think of modern technology as if it's NEW and EXCITING. We've had electricity for like 125 years used in mainstream. That's like a small blip on the radar map that is so miniscule it actually holds no importance what so ever. Like people that think that the US isn't nothing more than the Roman Empire v2.0 - all "good" things will eventually come to an end... and most likely, because of people's perception of
what once was of that "empire", things will be lost in the mix.
To me 300 years of quote un quote civilized society doesn't hold a fucking candle to the shit that has gone on in the past.
US Empire = 300 years
Roman Empire = 503 years give or take
People tend to forget shit from the past. The Ottoman Empire, Umayyad Caliphate, Mogols, Russians, Persians, etc.