Winchester Castle is a medieval building in Winchester, Hampshire, England. It was founded in 1067. Only the Great Hall still stands; it houses a museum of the history of Winchester. Around AD 70 the Romans constructed a massive earth rampart 800 ft long and 200 ft wide. On top of this they built a fort to protect the city of Venta Belgarum. This site wa…Winchester Castle is a medieval building in Winchester, Hampshire, England. It was founded in 1067. Only the Great Hall still stands; it houses a museum of the history of Winchester. Around AD 70 the Romans constructed a massive earth rampart 800 ft long and 200 ft wide. On top of this they built a fort to protect the city of Venta Belgarum. This site was chosen by William the Conqueror as the site of one of the first Norman castles in England.