Not sure what you are really asking. Rome has ruins deep underground.... and the Forum/Colosseum/Pantheon above ground. Over time things get burned/torn down/rebuilt and many modern cities are built on ancient sites. Many materials get put into other buildings and reused. Most of the city wall around Beijing was torn down and used in other things. A lot of the metal from building often got reused in other buildings. So why can't both explainations be right?