Verulamium Museum stands in the middle of the site of the Roman city of Verulamium. This was one of the largest towns in Roman Britain. Much of what remains of the Roman town now lies underneath Verulamium Park, but there are several parts of the site which have been excavated and can be viewed above ground: The Hypocaust (including an in situ mosaic); the Roman Theatre of Verulamium; and the remains of the Roman city walls and London gate.
This plan shows Verulamium in around AD 275. By this time several huge municipal buildings had been constructed, including the Basilica, which served as a town hall, religious centre and law court. It consisted of an enormous hall over 106 m (350 ft) long - the size of a cathedral. The Forum, a large colonnaded courtyard on the south-west side of the Basilica, was the main commercial and business centre of the town. Both of these stood very near to the present site of the Museum and St Michael's church.