There are a few remains of the Roman city visible , such as parts of the city walls , a hypocaust still in situ under a mosaic floor , and the theatre , which is on land belonging to the Earl of Verulam -- as well as items in the Museum ( below ) .
There are a few remains of the Roman city visible , such as parts of the city walls , a hypocaust ( heating system ) still in place under a mosaic floor . Remains of the theatre are on land belonging to the Earl of Verulam .