First Barons ' War The First Barons ' War ( 1215 – 17 ) was a civil war in the Kingdom of England in which a group of rebellious barons , led by Robert Fitzwalter and supported by a French army under the future Louis VIII of France , made war on King John of England . The war resulted from the king ' s refusal to accept and abide by the " Magna Carta " he had sealed on 15 June 1215 , and from the ambitions of the French prince , who dragged the war on after many of the rebel barons had made peace with John . Background . King John in June 1215 was forced to put his seal to " The Articles of the Barons " by a group of powerful barons who could no longer stand John ' s failed leadership and despotic rule . The king ' s Great Seal was attached to it on 15 June 1215 . In return , the barons renewed their oaths of fealty to King John on 19 July 1215 . A formal document to record the agreement was created by the royal chancery on 15 July : this was the original Magna Carta . " The law of the land " is one of the great watchwords of Magna Carta , standing in opposition to the king ' s mere will . Magna Carta of 1215 contained clauses which in theory noticeably reduced the power of the king , such as clause 61 , the " security clause " . This clause allowed a group of 25 barons to override the king at any time by way of force , a medieval legal process called " distraint " that was normal in feudal relationships but had never been applied to a king . After a few months of half - hearted attempts to negotiate in the summer of 1215 , open warfare broke out between the rebel barons and the king and his supporters . Course of events . Louis invited and welcomed . The war began over Magna Carta but quickly turned into a dynastic war for the throne of England . The rebel barons , faced with a powerful king , turned to Prince Louis , son and heir apparent of Philip Augustus , King of France , also a maternal grandson - in - law of the late English King Henry II . The Norman invasion had occurred only 150 years before , and the relationship between England and France was not so simply adversarial as it later became . The contemporary document called the annals of Waverley sees no contradiction in stating that Louis was invited to invade in order to " prevent the realm being pillaged by aliens " . At first , in November 1215 , Louis simply sent the barons a contingent of knights to protect London . However , even at that stage he also agreed to an open invasion , despite discouragement from his father the King of France and from the Pope . This came in May 1216 , when watchmen on the coast of Thanet detected sails on the horizon , and on the next day , the King of England and his armies saw Louis ' troops disembark on the coast of Kent . John decided to escape to the Saxon capital of Winchester , and so Louis had little resistance on his march to London . He entered London , also with little resistance , and was openly received by the rebel barons and citizens of London and proclaimed ( though not crowned ) king at St Paul ' s cathedral . Many nobles , including Alexander II of Scotland for his English possessions , gathered to give homage to him . Many of John ' s supporters , sensing a tide of change , moved to support the barons . Gerald of Wales remarked : " The madness of slavery is over , the time of liberty has been granted , English necks are free from the yoke . " On 14 June Louis captured Winchester ( John had already left ) and soon conquered over half of the English kingdom . First siege of Dover . In the meantime , the King of France taunted his son for trying to conquer England without first seizing its key : Dover . The royal castles at Canterbury and Rochester , their towns , and indeed most of Kent had already fallen to Louis but when he did move on to Dover Castle on 25 July , it was prepared . Its constable , Hubert de Burgh , had a well - supplied garrison of men . The first siege began on 19 July , with Louis taking the high ground to the north of the castle . His men successfully undermined the barbican and attempted to topple the castle gate , but De Burgh ' s men managed to repulse the invaders , blocking the breach in the walls with giant timbers . ( After the siege the weak northern gate was blocked and tunnels were built in that area , to St John ' s Tower , and the new Constable ' s Gate and Fitzwilliam ' s Gate were built . ) In the meantime , Louis ' s occupation of Kent was also being undermined by a guerrilla force of Weald en archers raised and led by William of Cassingham . After three months spent besieging the castle , and with a large part of his forces diverted by the siege , Louis called a truce on 14 October and soon after returned to London . Sieges of Windsor and Rochester . Apart from Dover , the only castle to hold out against Louis was that at Windsor , where 60 loyalist knights survived a two - month siege , despite severe damage to the structure of its lower ward ( immediately repaired in 1216 by Henry III , who further strengthened the defences with the construction of the western curtain wall , much of which survives today ) . This is possibly due to its having been already besieged by the barons in 1189 , less than 30 years earlier . In 1206 , John had spent £115 on repairs to Rochester Castle , and he had even preemptively held it during the year of the negotiations leading up to Magna Carta , but the Charter ' s terms had forced him to hand it back into the custody of Stephen Langton , archbishop of Canterbury , in May 1215 . The rebel barons had then sent troops under William d ' Aubigny to the castle , to whom its constable Reginald de Cornhill opened the castle ' s gates . Thus , during October 1215 on his marching from Dover to London , John found Rochester in his way and on 11 October began besieging it in person . The rebels were expecting reinforcements from London but John sent fire ships out to burn their route in , the city ' s bridge over the Medway . Robert Fitzwalter rode out to stop the king , fighting his way onto the bridge but eventually being beaten back into the castle . He also sacked the cathedral , took anything of value and stabled his horses in it , all as a slight to Langton . Orders were then sent to the men of Canterbury saying " We order you , just as you love us , and as soon as you see this letter , to make by day and night , all the pickaxes that you can . Every blacksmith in your city should stop all other work in order to make them and you should send them to us at Rochester with all speed " . Five siege engines were then erected and work carried out to undermine the curtain wall . By one of these means the king ' s forces entered and held the bailey in early November , and began attempting the same tactics against the keep , including undermining the south - east tower . The mine - roof was supported by wooden props , which were then set alight using pig - fat ( on 25 November 1215 John had sent a writ to the justiciar s saying " Send to us with all speed by day and night , forty of the fattest pigs of the sort least good for eating so that we may bring fire beneath the castle " , causing the whole corner of the keep to collapse . The rebels withdrew behind the keep ' s cross - wall but still managed to hold out . A few were allowed to leave the castle but on John ' s orders had their hands and feet lopped off as an example . Winter was now setting in , and the castle was only taken ( on 30 November ) by starvation and not by force . John set up a memorial to the pigs and a gallows with the intention of hanging the whole garrison , but one of his captains ( Savari de Mauléon ) persuaded him not to hang the rebels since hanging those who had surrendered would set a precedent if John ever surrendered – only one man was actually hanged ( a young bowman who had previously been in John ' s service ) . The remainder of the rebel barons were taken away and imprisoned at various royal - held castles , such as Corfe Castle . Of the siege – against only 100 rebels , and costing over a thousand pounds a day – the Barnwell chronicler wrote " No one alive can remember a siege so fiercely pressed and so manfully resisted " and that , after it , " There were few who would put their trust in castles " . John died the next year , so it fell to Henry III to repair the castle . He spent over £1 , 000 on rebuilding , with new stables and gateways , and a further ditch to strengthen the defences . A new chapel was built next to the Royal apartments in the bailey . The most notable surviving feature is the new south - east tower , which was built according to the latest defensive design and is three - quarters round to better deflect missile attack and work against attempts at undermining . Death of King John . On 18 October 1216 , John died at Newark Castle , Nottinghamshire , and with him the main reason for the fighting . Louis now seemed much more of a threat to baronial interests than John ' s nine - year - old son , Prince Henry . In fact Eleanor of Brittany , the grown daughter of John ' s late elder brother Geoffrey , imprisoned by John since 1202 , was another candidate for the crown as the rightful heiress to England since 1203 according to primogeniture , but the barons passed her over as they never recognised her claim , just like their ignorance of her when the Magna Carta was issued , leaving her still in prison . Pierre des Roches , Bishop of Winchester , and a number of barons rushed to have the young Henry to be crowned as king of England . London was held by Louis ( indeed , it was his seat of government ) and therefore could not be used for this coronation so , on 28 October 1216 , they brought the boy from the castle at Devizes to Gloucester Abbey in front of a small attendance presided over by a Papal Legate , Guala Bicchieri ( d . 1227 , bishop of Vercelli , papal legate in England 1216 – 18 ) . There , using as a crown a band of gold made from a necklace , they “ crowned ” Henry . On 12 November 1216 Magna Carta was reissued in Henry ' s name with some of the clauses , including clause 61 , omitted . The revised charter was signed by the young king ' s regent William Marshal . A great deal of the country was loyal to Prince Louis but the southwest of England and the Midlands favoured Henry . Marshal was highly respected and he asked the barons not to blame the child Henry for his father ' s sins . The prevailing sentiment , helped by self - interest , disliked the idea of depriving a boy of his inheritance . Marshal also promised that he and the other regents would rule by Magna Carta . Furthermore , he managed to get support from the Pope , who had already excommunicated Louis in any case . Louis ' s losses . William slowly managed to get most barons to switch sides from Louis to Henry and attack Louis . The two opposing sides fought for about a year . On 6 December 1216 Louis took Hertford Castle but allowed the defending knights to leave with their horses and weapons . He then took Berkhamsted Castle in late December , again allowing the royal garrison to withdraw honourably with their horses and weapons . By early 1217 , Louis decided to return to France for reinforcements , but had to fight his way to the south coast through loyalist resistance in Kent and Sussex , losing part of his force in an ambush at Lewes , with the remainder pursued to Winchelsea and only saved from starvation by the arrival of a French fleet . Since the truce had been arranged with Dover , the Dover garrison had repeatedly disrupted Louis ' s communication with France , and so Louis sailed back to Dover to begin a second siege . The French camp set up outside Dover Castle in anticipation of the new siege was attacked and burned by William of Cassingham just as the fleet carrying the reinforcements arrived , and so Louis was forced to land at Sandwich and march to Dover , where he began a second siege in earnest on 12 May 1217 . However , this new siege diverted so much of Louis ' s forces that William Marshal and Falkes de Breauté were able to attack and heavily defeat pro - Louis barons at Lincoln Castle on 15 May or 20 May 1217 , in what became known as the Second Battle of Lincoln . William Marshal prepared for a siege against London next . But in the meantime , Louis suffered two more heavy defeats , this time at sea , at the Battle of Dover and Battle of Sandwich in the Straits of Dover , this time at the hands of Guillaume ' s ally and Dover ' s constable , Hubert de Burgh . Louis ' new reinforcement convoy , under Eustace the Monk , was destroyed , making it nearly impossible for Louis to continue fighting . Peace . After a year and a half of war , most of the rebellious barons had defected and so Louis VIII had to give up his claim to be the King of England by signing the Treaty of Lambeth on 11 September 1217 . Louis accepted a symbolic sum to relinquish his English dominions and returned home . Though it was not in the treaty , it was often reported that Louis would try to convince the King of France , his father , to give to the one known as Henry what he had conquered from his father John . In popular culture . " Ironclad " , a 2011 film starring Paul Giamatti and James Purefoy , chronicles the siege of Rochester Castle . " Robin Hood " , a 2010 film , is loosely based on the events surrounding the Barons ' War .