The Roman amphitheatre was filled with buildings over the years, but in 1830 the place was cleared and houses were built on the fundaments of the amphitheatre, creating an oval square, first used for the daily market.
Pictures from 1977:
commons.wikimedia.org/wiki/File:Paolo_Monti_-_Servizio_fo...
commons.wikimedia.org/wiki/File:Paolo_Monti_-_Servizio_fo...