The battle was part of a civil war – the Second Barons’ War – which resulted from dissatisfaction with King Henry III. Henry had spent a considerable amount of money in unsuccessful attempts to claim (or reclaim) land in France and Italy. In addition, he’d shown favouritism to his French relatives rather than trusting English noblemen. English barons responded by insisting on the creation of a government with members chosen by the barons alongside those chosen by the king. Although the agreement – known as the Provisions of Oxford – became law in 1258, it was later revoked by Henry. As a result, civil war broke out between Royalist forces led by the king’s son (Prince Edward, later to become King Edward I) and rebel barons led by Simon de Montfort.
Simon de Montfort, the 6th Earl of Leicester, had previously been a supporter of Henry’s and was married to Henry’s sister Eleanor. His forces were in London when the Royalist army arrived in Lewes. King Henry camped at St Pancras Priory, while Prince Edward went to the castle with his cavalry. De Montfort came to town and offered to negotiate but his terms were rejected by the King. The following battle saw the Royalist forces, despite being larger than de Montfort’s, make tactical errors that led to their defeat. Lewes was burned and King Henry III surrendered.
Henry signed the Mise of Lewes, an interim settlement, and Simon de Montfort went on to set up what’s sometimes described as the first English parliament.
However, in-fighting between former allies, coupled with Prince Edward’s escape from captivity, resulted in de Montfort’s death at the Battle of Evesham just over a year later.