 King John undertook some building works at Windsor , but primarily to the accommodation rather than the defences . The castle played a role during the revolt of the English barons : the castle was besieged in 1214 , and John used the castle as his base during the negotiations before the signing of the Magna Carta at nearby Runnymede in 1215 . In 1216 the castle was besieged again by baronial and French troops under the command of the Count of Nevers , but John 's constable , <unk> de <unk> , successfully defended it . 
