Basing House is an early 12th century earth and timber ringwork and bailey fortress, founded by the de Port family. In 1261, Robert de St John founded the stone castle, when adding a keep and a gatehouse encased by a heighten rampart but the outer defences remained of timber. In 1531, Sir William Paulet, constructed the Citadel inside the ringwork, when he was granted a licence to crenellate. Later to the north east of the ringwork, he constructed a brick Tudor palace, comprising of a series of rectangular buildings, arranged around a central courtyard. In 1643, Civil War earthwork defences, were added to the castle, which was under siege, until being stormed by Oliver Cromwell in 1645. The successor to Olivers Battery, the castle was then slighted, with the remainder being demolished after the Restoration. Both buildings now survive as ruins.