Even with today's technology, man cannot replicate the building of the Great Pyramid of Giza. The Chinese tried, and failed. Hauling fifty tonne stone blocks, perfectly cut, was a feat that even the ingenious Chinese weren't up to. So was the Great Pyramid actually built by man, as is the established doctrine? Or was it the work of extraterrestrials, hovering above the Giza Plateau lowering the blocks into place utilising some sort of levitation technology that we are not yet privy to? Perhaps the Pyramids are natural formations? Now that's a theory we have yet to hear.