Bristol Castle Bristol Castle was a Norman castle built for the defence of Bristol . Remains can be seen today in Castle Park near the Broadmead Shopping Centre , including the sally port . History . The first castle built at Bristol was a timber motte and bailey , presumably erected on the command of William the Conqueror , who owned Bristol . One of William ' s closest allies , Geoffrey de Montbray , Bishop of Coutances , appears to have had control of the castle in William ' s name . The Domesday Book notes that he received part of the king ' s income from the borough . The castle is first mentioned in 1088 , when Geoffrey used it as a base in his rebellion against William Rufus . After William triumphed , the English lands of the rebels were redistributed to his loyal followers . Among them was Robert Fitzhamon , who gained a large swathe of Gloucestershire , including Bristol Castle . His eldest daughter Mabel married Robert , illegitimate son of Henry I . She brought him the honour of Gloucester on the death of her father in 1107 . So he is generally known as Robert of Gloucester . By this time many of the first wave of Norman timber castles were being replaced in stone . Bristol Castle was a fine example with curtain walls and a great keep . It seems that Robert of Gloucester was the man responsible . The castle was built on a strategic site to the east of the town , between the River Avon and the River Frome , which was partly diverted to form the castle moat . This great fortress was to play a key role in the civil wars that followed the death of Henry I of England . Henry ' s only legitimate son William drowned in 1120 , so Henry eventually declared his one legitimate daughter Matilda his heir . However her cousin , Stephen of Blois usurped the throne on Henry ' s death in 1135 . Matilda ' s half - brother Robert of Gloucester became her trusted right - hand man – the commander of her troops . Rebels rallied to his castle at Bristol . Stephen reconnoitred Bristol in 1138 but decided that the town was impregnable . As his chronicler reported : " On one side of it , where it is considered more exposed to siege and more accessible , a castle rising on a vast mound , strengthened by wall and battlements , towers and divers engines , prevents an enemy ' s approach . " After Stephen was captured in 1141 , he was imprisoned in Bristol Castle until Robert of Gloucester was also captured and an exchange of prisoners was made . The castle was later taken into royal hands . Henry III , educated there in his youth , spent lavishly on it , adding a barbican before the main west gate , a gate tower , and magnificent great hall . From 1224 , Eleanor of Brittany , the rightful heiress to England according to primogeniture and thus a potential threat to the throne , was strictly confined in the castle under relatively comfortable conditions and ended up there . The two young sons of Dafydd ap Gruffydd , the last princes of Gwynedd , were imprisoned for life in Bristol Castle after Edward I ' s conquest of Wales in 1283 . William le Scrope , Sir John Bussy and Sir Henry Green were executed there without trial in June 1399 by the Duke of Hereford , soon to be King Henry IV of England , after the latter ' s successful return from exile . The first detailed description of the castle was written in 1480 . By the time the antiquary John Leland visited " c " . 1540 , Bristol castle was showing signs of neglect . It had " two courts , and in the north - west part of the outer court there is a large keep with a dungeon , said to have been built of stone brought by the red Earl of Gloucester from Caen in Normandy . In the other court is an attractive church and many domestic quarters , with a great gate on the south side , a stone bridge and three ramparts on the left bank leading to the mouth of the Frome . Many towers still stand in both the courts , but they are all on the point of collapse . " . By the sixteenth century the castle had fallen into disuse , but the City authorities had no control over royal property and the precincts became a refuge for lawbreakers . In 1630 the city bought the castle and when the Civil War broke out the city took the Parliamentary side and partly restored the castle . However Royalist troops occupied Bristol and eventually Oliver Cromwell ordered the destruction of the castle . The castle was demolished in 1656 , according to Millerd ' s map of Bristol ( above right ) . However one octagonal tower survived until it was torn down in 1927 . It was sketched by Samuel Loxton in 1907 . There are some remains of the banqueting hall incorporated in an existing building . The castle moat was covered over in 1847 but still exists and is mainly navigable by boat , flowing under Castle Park and into the Floating Harbour . The western section is a dry ditch and a sally port into the moat survives near St Peter ' s Church . The area was redeveloped for commerce , and later largely destroyed in the ' Bristol Blitz ' . It was subsequently redeveloped as a public open space , Castle Park . Today . It is a Scheduled Ancient Monument .