Battle of Lewes The Battle of Lewes was one of two main battle s of the conflict known as the Second Barons ' War . It took place at Lewes in Sussex , on 14 May 1264 . It marked the high point of the career of Simon de Montfort , 6th Earl of Leicester , and made him the " uncrowned King of England " . Henry III left the safety of Lewes Castle and St . Pancras Priory to engage the Barons in battle and was initially successful , his son Prince Edward routing part of the Baronial army with a cavalry charge . However Edward pursued his quarry off the battlefield and left Henry ' s men exposed . Henry was forced to launch an infantry attack up Offham Hill where he was defeated by the Barons ' men , defending the hilltop . The royalists fled back to the castle and priory and the King was forced to sign the Mise of Lewes , ceding many of his powers to de Montfort . Background . Henry III was an unpopular monarch due to his autocratic style , displays of favouritism and his refusal to negotiate with his Barons . The Barons eventually imposed a constitutional reform known as the Provisions of Oxford upon Henry that called for a thrice - yearly meeting led by Simon de Montfort to discuss matters of government . Henry sought to escape the restrictions of the Provisions and applied to Louis IX of France to arbitrate in the dispute . Louis agreed with Henry and annulled the provisions . De Montfort was angered by this and rebelled against the king along with other barons in the Second Barons ' War . The war was not initially openly fought , each side toured the country to raise support for their army . By May the King ' s force had reached Lewes where they intended to halt for a while to allow reinforcements to reach them . The King encamped at St . Pancras Priory with a force of infantry , but his son , Prince Edward ( later King Edward I ) commanded the cavalry at Lewes Castle to the north . De Montfort approached the King with the intention of negotiating a truce or failing that to draw him into open battle . The King rejected the negotiations and de Montfort moved his men from Fletching to Offam Hill , a mile to the north - west of Lewes , in a night march that surprised the royalist forces . Deployment . The royalist army was up to twice the size of de Montfort ' s . Henry held command of the centre ; with Prince Edward , William de Valence , 1st Earl of Pembroke and John de Warenne , 6th Earl of Surrey on the right ; and Richard , 1st Earl of Cornwall and his son , Henry of Almain on the left . , The Barons held the higher ground , overlooking Lewes and had ordered their men to wear white crosses as a distinguishing emblem . De Montfort split his forces into four parts , giving his son , Henry de Montfort command of one quarter ; Gilbert de Clare with John FitzJohn and William of Montchensy another ; a third portion consisting of Londoners was placed under Nicholas Seagrave whilst de Montfort himself led the fourth quarter with Thomas of Pelveston . Battle . The Baronial forces commenced the engagement with a surprise dawn attack on foragers sent out from the Royalist forces . The King then made his move . Edward ' s led a cavalry charge against Seagrave ' s Londoners , placed on the left of the Baronial line , that caused them to break and run to the village of Offham . Edward pursued his foe for some four miles , leaving the King unsupported . Henry was forced to launch an attack with his centre and right divisions straight up Uffham Hill into the Baronial line which awaited them at the defensive . Cornwall ' s division faltered almost immediately but Henry ' s men fought on until compelled to retreat by the arrival of de Montfort ' s men that had been held as the Baronial reserve . The King ' s men were forced down the hill and into Lewes where they engaged in a fighting retreat to the castle and priory . Edward returned with his weary cavalrymen and launched a counterattack but upon locating his father was persuaded that , with the town ablaze and many of the King ' s supporters fled , it was time to accept de Montfort ' s renewed offer of negotiations . The Earl of Cornwall was captured by the Barons when he was unable to reach the safety of the priory and , being discovered in a windmill , was taunted with cries of " Come down , come down , thou wicked miller ! " Aftermath . The King was forced to sign the so - called Mise of Lewes . Though the document has not survived , it is clear that Henry was forced to accept the Provisions of Oxford , while Prince Edward remained hostage to the barons . This put Montfort in a position of ultimate power , which would last until Prince Edward ' s escape , and Montfort ' s subsequent defeat at the Battle of Evesham in August 1265 . Location . There remains some uncertainty over the location of the battle with Offham Hill ' s eastern and lower slopes covered by modern housing . The top and southern slopes remain accessible by footpaths through agricultural land and the ruins of the priory and castle are also open to visitors .