I think it was aliens! Actually not really but a tiny bit maybe. And not that aliens built them, but that knowledge of how to do certain things came from aliens or even earlier humans and maybe was lost (ok I've been watching too much Why Files).

The reason why for me is the large stone size. Understanding simple geometry is one thing, sure, but moving thousands of multi-ton blocks miles and stacking them with precision is another. If it's so easy, I'd like to see a demonstration. We should be able to do it in a year or so by now right?

Also, I find it interesting that we can see with satellites roads used thousands of years ago buried by the Amazon, why doesn't there seem to be remnants of the roads and massive ramps that it's claimed were used to transport these massive blocks for the decades it took to build the pyramids? Also, I'd imagine a massive earthen ramp large enough to do the job would put a good amount of force on the pyramid that could push blocks out of position but that doesn't seem to have happened.