Oxford Castle Oxford Castle is a large , partly ruined Norman medieval castle on the western side of central Oxford in Oxfordshire , England . Most of the original moat ed , wooden motte and bailey castle was replaced in stone in the 11th century and played an important role in the conflict of the Anarchy . In the 14th century the military value of the castle diminished and the site became used primarily for county administration and as a prison . Most of the castle was destroyed in the English Civil War and by the 18th century the remaining buildings had become Oxford ' s local prison . A new prison complex was built on the site from 1785 onwards and expanded in 1876 ; this became HM Prison Oxford . The prison closed in 1996 and was redeveloped as an hotel . The medieval remains of the castle , including the motte and St George ' s Tower and crypt , are Grade I listed buildings and a Scheduled Monument . History . Construction . According to the " Abingdon Chronicle " , Oxford Castle was built by the Norman baron Robert D ' Oyly the elder from 1071 – 73 . D ' Oyly had arrived in England with William I in the Norman Conquest of England in 1066 and William the Conqueror granted him extensive lands in Oxfordshire . Oxford had been stormed in the invasion with considerable damage , and William directed D ' Oyly to build a castle to dominate the town . In due course D ' Oyly became the foremost landowner in Oxfordshire and was confirmed with a hereditary royal constableship for Oxford Castle . Oxford Castle is not among the 48 recorded in the Domesday Book of 1086 , but not every castle in existence at the time was recorded in the survey . D ' Oyly positioned his castle to the west side of the town , using the natural protection of a stream of the River Thames on the far side of the castle , now called Castle Mill Stream , and diverting the stream to produce a moat . There has been debate as to whether there was an earlier English fortification on the site , but whilst there is archaeological evidence of earlier Anglo - Saxon habitation there is no conclusive evidence of fortification . Oxford Castle was clearly an " urban castle " but it remains uncertain whether local buildings had to be demolished to make room for it . The Domesday Book does not record any demolition , so the land may have already been empty due to the damage caused by the Norman seizure of the town . Alternatively the castle may have been imposed over an existing street front which would have required the demolition of at least several houses . The initial castle was probably a large motte and bailey , copying the plan of the castle that D ' Oyly had already built away at Wallingford . The motte was originally about high and wide , constructed like the bailey from layers of gravel and strengthened with clay facing . There has been debate over the sequencing of the motte and the bailey : it has been suggested that the bailey may have built first , which would make the initial castle design a ringwork rather than a motte and bailey . By the mid - 12th century Oxford Castle had been significantly extended in stone . The first such work was St George ' s Tower , built of coral rag stone in 1074 , at the base and tapering significantly toward the top for stability . This was the tallest of the castle ' s towers , possibly because it covered the approach to the old west gate of the city . Inside the walls the tower included a crypt chapel , which may be the site of a previous church . The crypt chapel originally had a nave , chancel and an apsidal sanctuary . It is a typical early Norman design with solid pillars and arches . In 1074 D ' Oyly and his close friend , Roger d ' Ivry endowed a chapel with a college of priests . At an early stage it acquired a dedication to Saint George . Early in the 13th century the wooden keep on top of the motte was replaced with a ten - sided stone shell keep , , closely resembling those of Tonbridge and Arundel Castle s . The keep enclosed a number of buildings , leaving an inner courtyard only across . Within the keep , stairs led down to an underground wide stone chamber , with an Early English hexagonal vault and a deep well providing water in the event of siege . Role in the Anarchy and Barons War . Robert D ' Oyly the younger , Robert D ' Oyly the elder ' s nephew , had inherited the castle by the time of the civil war of the Anarchy in the 1140s . After initially supporting King Stephen , Robert declared his support for Empress Matilda , Stephen ' s rival for the throne , and in 1141 the Empress marched to Oxford to base her campaign at the castle . Stephen responded by marching unexpectedly from Bristol in December , attacking and seizing the town of Oxford and besieging Matilda in the castle . Stephen set up two siege mounds beside the castle , called Jew ' s Mount and Mount Pelham , on which he placed siege engines , largely for show , and proceeded to wait for Matilda ' s supplies to run low over the next three months . Stephen would have had difficulty in supplying his men through the winter period , and this decision shows the apparent strength of Oxford Castle at the time . Matilda responded by escaping from the castle ; the popular version of this has the Empress waiting until the Castle Mill Stream was frozen over and then dressed in white as camouflage in the snow , being lowered down the walls with three or four knights , before escaping through Stephen ' s lines in the night as the king ' s sentries tried to raise the alarm . The chronicler William of Malmesbury , however , suggests Matilda did not descend the walls , but instead escaped from one of the gates . Matilda safely reached Abingdon - on - Thames and Oxford Castle surrendered to Stephen the next day . Robert had died in the final weeks of the siege and the castle was granted to William de Chesney for the remainder of the war . At the end of the war the constableship of Oxford Castle was granted to Roger de Bussy before being reclaimed by Henry D ' Oyly , Robert D ' Oyly the younger ' s son , in 1154 . In the Barons ' War of 1215 – 17 the castle was attacked again , prompting further improvements in its defences . In 1220 Falkes de Breauté , who controlled many royal castles in the middle of England , demolished the Church of St Budoc to the south - east of the castle and built a moated barbican to further defend the main gate . The remaining wooden buildings were replaced in stone , including the new Round Tower which was built in 1235 . King Henry III turned part of the castle into a prison , specifically for holding troublesome University clerks , and also improved the castle chapel , replacing the older barred windows with stained glass in 1243 and 1246 . Due to the presence of Beaumont Palace to the north of Oxford , however , the castle never became a royal residence . 14th – 17th centuries . By 1327 the fortification , particularly the castle gates and the barbican , was in poor condition and £800 was estimated to be required for repairs . From the 1350s onwards the castle had little military use and was increasingly allowed to fall into disrepair . The castle became the centre for the administration of the county of Oxford , a jail , and a criminal court . assizes were held there until 1577 , when plague broke out in what became known as the " Black Assize " : the Lord Lieutenant of Oxfordshire , two knights , eighty gentlemen and the entire grand jury for the session all died , including Sir Robert D ' Oyley , a relative of the founder of the castle . Thereafter assizes ceased to be held at the castle . By the 16th century the barbican had been demolished to make way for houses and the moat had begun to be occupied with housing . By 1600 the moat was almost entirely silted up and houses had been built all around the edge of the bailey wall . In 1611 King James I sold Oxford Castle to Francis James and Robert Younglove , who in turn sold it to Christ Church College in 1613 . The college then leased it to a number of local families over the coming years . By this time Oxford Castle was in a weakened state , with a large crack running down the side of the keep . In 1642 the English Civil War broke out and the Royalist s made Oxford their capital . Parliamentary forces successfully besieged Oxford in 1646 and the city was occupied by Colonel Ingoldsby . Ingoldsby improved the fortification of the castle rather than the surrounding town , and in 1649 demolished most of the medieval stonework , replacing it with more modern earth bulwark s and reinforcing the keep with earth works to form a probable gun - platform . In 1652 , in the third English Civil War , the Parliamentary garrison responded to the proximity of Charles II ' s forces by pulling down these defences as well and retreating to New College instead , causing great damage to the college in the process . In the event , Oxford saw no fresh fighting ; early in the 18th century , however , the keep was demolished and the top of the motte landscaped to its current form . Role as prison . After the Civil War , Oxford Castle served primarily as the local prison . As with other prisons at the time , the owners , in this case Christ Church College , leased the castle to wardens who would profit by charging prisoners for their board and lodging . The prison also had a gallows to execute prisoners , such as Mary Blandy in 1752 . For most of the 18th century , the castle prison was run by the local Etty and Wisdom families and was in increasing disrepair . In the 1770s the prison reformer John Howard visited the castle several times , and criticised its size and quality , including the extent to which vermin infested the prison . Partly as a result of this criticism , it was decided by the County authorities to rebuild the Oxford Prison . In 1785 the castle was bought by the Oxford County Justices and rebuilding began under the London architect William Blackburn . The wider castle site had already begun to change by the late 18th century , with New Road being built through the bailey and the last parts of the castle moat being filled in to allow the building of the new Oxford Canal terminus . Building the new prison included demolishing the old college attached to St George ' s chapel and repositioning part of the crypt in 1794 . The work was completed under Daniel Harris in 1805 . Harris gained a reasonable salary as the new governor and used convict labour from the prison to conduct early archaeological excavations at the castle with the help of the antiquarian Edward King . In the 19th century the site continued to be developed , with various new buildings built including the new County Hall in 1840 – 41 and the Oxfordshire Militia Armoury in 1854 . The prison itself was extended in 1876 , growing to occupy most of the remaining space . In 1888 national prison reforms led to the renaming of the county prison as HM Prison Oxford . Today . Since 1954 the two oldest parts of the castle have been Grade I listed buildings : the 11th - century motte with its 13th - century well - chamber , and the 11th - century St George ' s tower with its crypt chapel and the 18th - century D - wing and Debtors ' Tower . The site is protected as a Scheduled Monument . The prison was closed in 1996 and the site reverted to Oxfordshire County Council . The Oxford Prison buildings have since been redeveloped as a shopping and heritage complex , with guided tours of the historic buildings and open courtyards for markets and theatrical performances . The complex includes a hotel in the Malmaison chain , Malmaison Oxford , occupying a large part of the former prison blocks , with cells converted as guest rooms . However , those parts of the prison associated with corporal or capital punishment have been converted to offices rather than being used for guests . The mixed - use heritage project won the RICS Project of the Year Award 2007 .