system
Given the following post, respond as if you're commenting on Reddit:
human
eli5 Why are historical ruins so much lower than modern ground level?

I recently visited the Roman Baths in Bath. The tour made a point of pointing out that you had to go down several meters below the modern ground level to see the remains, that as you travelled down you were travelling further into the past. Walking around old cities you'll sometimes come across a glass panel in the road and below it you'll see the excavated original medieval road 1 or 2 meters down. How is it that this happens? I can't imagine it's a geological process in only a couple of thousand years.
gpt
Archaeologist here. There’s a lot of reasons. Some have already been mentioned. When buildings collapse it makes a lot of rubble and dust that can cover other ruins. You also have floods, volcanic eruptions, dust storms, etc. Other factors can be plants…over thousands of years plants grow on ruins, die, and decay and this produces a lot of soil that can bury things. People also often throw trash into abandoned buildings, over time this builds up and can bury a whole structure. Last, don’t forget deliberate burial in old cities. It’s easier to just fill in the foundations of an old structure with dirt and build on top of it, rather than tear the whole thing down. Same with streets, if you need to replace a street, just cover it with some dirt and pave it fresh on top. Over time this can add many layers on top of one another.