Doug Miller wrote:

....
pyramids he examined the blocks and concluded that it's _not_natural_stone_.
He says it's actually _concrete_ and they were cast in place.

Not so far-fetched as it might seem, either: ...


Except there's geology that apparently traces the stones back to the
Giza plateau from whench they were quarried...

http://www.harvard-magazine.com/on-line/070391.html