Banbury Castle Banbury Castle was a medieval castle that stood near the centre of the town of Banbury , Oxfordshire . Historian John Kenyon notes that the castle is " remarkable for its early concentric shape " . History . Banbury Castle was built in 1135 by Alexander , Bishop of Lincoln , in a motte and bailey design . The castle was later confiscated from Alexander by King Stephen in 1139 , but was returned to the bishop later that year and mostly remained in the hands of later bishops until 1547 . The castle was protected by a castle - guard drawn from estates around Banbury . The castle was strengthened between 1201 - 7 during the reign of King John . The castle was subsequently completely rebuilt ; earlier historians had concluded that the rebuilding occurred in the late 13th century , but archaeological excavations in the 1970s demonstrated that the work occurred between 1225 - 50 . The new castle had a concentric pentagonal plan , with thick , embanked walls . The castle had a gatehouse , although later damage means that its design remains uncertain . Historian John Kenyon concludes that Banbury Castle is " remarkable for its early concentric shape " , which is usually seen in somewhat later castles such as Harlech or Beaumaris . By the second half of the 13th century the castle was being used as a prison by the bishops of Lincoln . The castle was bought by the Edward Seymour , the Duke of Somerset , in 1547 ; it passed shortly afterwards to John Dudley , the Duke of Northumberland , who sold it to the Crown in 1551 . Shortly after this the prison in the castle diminished in size , vanishing entirely by the 1560s . The prison was recreated in the 1580s , however , for holding recusant s , that is to say Roman Catholics who refused to attend Church of England services as was required by law . In 1595 Banbury Castle was leased to Richard Fiennes , the lord of Saye and Sele . In 1642 the English Civil War broke out between the Royalist supporters of Charles I and the supporters of Parliament . Banbury Castle was initially held by William Fiennes , the son of Richard , for Parliament and the castle was hastily refortified . After the battle of Edgehill , Charles marched south and forced the surrender of the castle and its stock of 1 , 500 firearms . The fortifications were strengthened and in 1644 the castle was besieged again , this time by Parliamentary forces under the command of William Fiennes . The royal governor , the 18 - year - old William Compton , held out between July and October , when Compton ' s brother , James , relieved the siege . In November , Charles I dined in the castle . In January 1646 Sir Edward Whalley placed the castle under siege again with a force of 3 , 000 men ; the Royalist cause was collapsing , and in May Compton and his force of 300 men surrendered . After the war the castle itself was slighted , or deliberately demolished , in 1648 to prevent its further use ; Fiennes was paid £2 , 000 by Parliament in compensation . Stones from the castle were later used to build houses in the town . Today . Nothing can now be seen of Banbury Castle , whose location is marked by Castle Street . The site was excavated in 1973 – 74 .