That’s how it usually goes, either the outer circuit of the circus and amphitheaters are used as support walls for housing, the entire thing is turned into a ramshackle fortress for a feudal petty noble or the flat space is used for farming by local peasantry who don’t need to clear any rubble.

Here’s a visual reconstruction for comparison of the city during Roman times by archaeologist Jean Claude Golvin

Also, for an interesting historical sweep of where things turned out, here’s a pictoral map made of the city in 1953, still largely bombed out following WWII.