Referring to sacking cities, maybe they could even disappear if the population goes too low and there's a Town (or Village, maybe) nearby? Since I tend to play from 3000BC for different scenarios, it's always been bugging me that I keep seeing the same cities over and over. I would very much like for cities to experience pillaging and possibly natural disasters (such as earthquakes, tornadoes, tsunamis and so forth) to actually represent a city's decline and the movement of the center of power in the region to another place. The old city could transform into a village or something of this sort and the new could keep an amount of the old city's population, culture and buildings, but change its location and name.
EDIT : Additionally, I don't find it adequate for regions to become barren just because all the nearby cities have been razed and so the area doesn't de facto belong to anyone. Perhaps it's okay with harsh climate, but I think that if a core area of a civ doesn't have a single city within its range and the civ has already spawned, there should be a semi-random independent city appearing.