 The Roman Museum houses an in situ mosaic pavement dating from around 300 AD . Surviving structures from the Roman times include Queningate , a blocked gate in the city wall , and the Dane John Mound , once part of a Roman cemetery . The Dane John Gardens were built beside the mound in the 18th century , and a memorial was placed on the mound 's summit . A windmill was on the mound between 1731 and 1839 . 
