Apropos the 'worm cast' aspect of sinking structures. Obviously that's a little simplistic, with a variety of erosional aspects all playing a part...
I have asked a number of geologists and archaeologists for an opinion on the following and never had anything other than an evasive reply.
I was in Rome a few years back and marvelling at the fact that the renaissance remains stand 16ft or so above the Roman Forum. It started me wondering how people related to buildings that were gradually disappearing below ground. The area has always been populated so generations of people watched the earth climb over the doorstep, up the walls, over the roof etc.
Why? Why didn't they keep it clear and live in the houses? At what point did those Roman remains lose their human connection? It confuses the hell out of me (and apparently the experts who never answer). Any of you clever folk have an idea?
Rome was invaded many times since the forum was built; the Celts invaded in 387BC thus earning the title "Founders of Europe". Centuries later the Barbarians (Ostrogoths, Vandals etc) plundered Rome, so perhaps ruined buildngs were used as footings or foundations for what followed. The Renaissance Romans would not have had the equipment to do anything else than build on top of what was already there ...(hope one of the many people with 'dig' knowledge comes back on this one).
I have only been to Rome once and it is an astonishing city of the ancient mixed in the with modern. It was fascinating that one of the bridges we drove over was a couple of thousand years old.