What seems more likely to you, the idea that our ancient ancestors created these buildings and somehow through the sands of time the blueprints were lost, or that another intelligent species, something which we have never known having lived 2,000 years of recordable history on the planet, came, created, and left without a shred of evidence as to how they did it?
More than just buildings, if you're talking about our genetic makeup, the stuff we're actually made of, what we consist of, if you can't prove it, like I said, what difference does it make?
It's an unfortunate consequence of the life we live, that which you can't prove doesn't matter. If you can suspend your belief to accept a belief without sufficient evidence, more power to you, ignorance is bliss, but for those of us that can't, it's essentially worthless. Agree?