Kang of Pang
I was going to guess, "slavery."
I've often thought this was the case for all these really awesome forms of rock work. Limestone is a sedimentary rock. It isn't too far fetched that you could use knowledge on how a sedimentary rock is formed in order to make one. Of course I would guess that during the time of their construction, they probably weren't as strong as real limestone. But how much time does sedimentary rock need to be hard? Its known that you can create Limestone through evaporation in arid environments.What did we have available to us 10,000 years ago? Some wood, some water, and the makings of cement.