I'm reading some books that describe site excavations. The archaeologists dig layers of dirt up to get to the ancient settlements many feet below. I'm wondering how they get buried in the first place. There are some photographs that look like a town from the ninth century with a series of rooms that look more than ten feet deep. Did people dig cellars or below-ground rooms? Or was the ground level much lower then than it is today? But even closer to the surface, where is all the soil coming from? How do these places get buried?