Do I have this right? When looking at images of ancient ruins, such as at http://www.mccullagh.org/photo/1ds-4/roman-city-ruins-dougga, I was left wondering where the debris has gone to. What I gather from reading various articles is that these missing walls of marble and stone were largely scavenged. So, people carted away the fallen walls to make their own buildings, or ground them up for lime or cement? Is this the main reason why ancient ruins are so empty?