Odiham Castle Odiham Castle ( also known locally as King John ' s Castle ) is a ruined castle situated near Odiham in Hampshire , United Kingdom . It is one of only three fortresses built by King John during his reign . The site was possibly chosen by King John because he had visited the area in 1204 and it lay halfway between Windsor and Winchester . Construction . Odiham Castle was built on of land acquired from local lord , Robert the Parker ; utilising a modified bend of the River Whitewater . The castle , which took seven years to complete , had a two - storey stone keep and a square moat . There were also raised banking and palisades . Notably the stronghold also had a " domus regis " or ' king ' s house ' . Scrolls held in the public records office reveal that total expenditure between 1207 and 1214 , when work ceased , amounted to £1 , 000 ( equivalent of £11 . 4m in 2009 ) . History . In 1215 it was from either Odiham or Windsor that King John rode out to Runnymede where he met the barons and signed the Magna Carta . A year later Odiham Castle was captured by the French after a two - week siege during the First Barons ' War in 1216 . The garrison of just 13 surrendered on July 9 , 1216 . At some point over the next 9 years the keep was completely rebuilt possibly due to the damage done to it by the French forces . At the same time the mound on which the keep sat was raised by 5 meters and an inner moat surrounding the keep was added to the defenses . Odiham Castle might have become one of the most important strongholds in England . In 1238 Simon de Montfort married King John ' s daughter Eleanor just two years after she had been granted Odiham by her brother , King Henry III . In the following year a kitchen was added on a bridge over the inner moat and a new hall was added on the outside of the keep . During the same period a second building was constructed over the moat this time on the south eastern side of the keep to provide extra living space . In 12 63 De Monfort rebelled against Henry and died at the Battle of Evesham in 1265 and Eleanor was exiled . Odiham Castle was again retained by the Crown . The castle was also involved in the rebellion led by the powerful Despenser family against Roger Mortimer and Queen Isabella of France , the wife of Edward II . During the fourteenth century Odiham hosted Parliament . Scottish King David II , after his capture at the Battle of Neville ' s Cross in 1346 , was also imprisoned here for 11 years . However he was held under light guard and was allowed to keep a household . Using the castle as a prison seems to have been common practice during the 13th and 14th centuries with the nearby Manor of Greywell required to provide guards one night in three . By the 15th century Odiham was used only as a hunting - lodge . In 1605 the former royal castle was described as a ruin . In 1792 the Basingstoke Canal was built through the southern corner of the bailey . Present day . Odiham Castle is open to the public . The only visible remains are part of the octagonal keep and outlying earthworks . In September 2007 Hampshire County Council undertook a restoration of the shell keep under guidance from English Heritage . The most southerly corner of the moat survives in the form of a small overgrown pond on the opposite side of the canal from the rest of the castle . Restoration . Restoration work began in September 2007 to consolidate the ruins and carry out extensive work on improving the site .