For a long time, people couldn't figure out how the Easter Islanders were able to move the statues from the quarries to their final destinations. The hint was in the oral history of the Rapa Nuians: the statues walked. That was dismissed as primitive stories. And then:
View: https://www.youtube.com/watch?v=yvvES47OdmY
There's still on-going debate on how the granite blocks of the pyramids could be moved into place. They discovered recently that a channel of the Nile ran right up to the Giza plateau. That would answer how the blocks were moved from the quarries hundreds of miles away. But then there's these unexplained shafts cut into the bedrock going right up to the pyramids in a line, with hints that there's a tunnel system beneath them:
View: https://www.youtube.com/watch?v=XRpZJdn5tCs
My pet theory is that the Egyptians used hydraulic-powered cranes. They'd flood the shafts to lift the counterweights and then drain them to raise and move the stones.
Something more recent, but a cool demonstration of what comparatively "primitive" people to us were able to accomplish with hydraulics:
View: https://www.youtube.com/watch?v=37JtQl1gUtA
Dave's right, it's amazing what people can accomplish when they're put to focus on a single-minded goal.