If you leave ground alone all sort of things grow on it or lay on it. Dirt, mud, leaves etc. Soil grows at about 1 mm per year. 1 meter in 1000 years.

Historically cities were hit by floods and wars and new buildings were built on top of the foundations of old ones. We had an article about that church in Rome built over another roman church built over another roman church, etc. down to an old temple on a spring, or something like that.