The Battle of Lewes was a battle that took place at Lewes in Sussex, from May 12 - May 14, 1264. It was the high point of the career of Simon de Montfort, Earl of Leicester, and made him the "uncrowned king of England".
The battle occurred because of the vacillation of King Henry III of England, who was refusing to honour the terms of the Provisions of Oxford, an agreement he had signed with his barons, led by de Montfort, in 1258. The king had taken refuge at a priory, but his son, Prince Edward (later King Edward I of England) held Lewes Castle. A night march enabled de Montfort's forces to surprise Edward and take the high ground of the Sussex Downs, overlooking the town of Lewes, in preparation for battle. They wore white crosses as their distinguishing emblem.
Edward commanded an army twice the size of de Montfort's. Having led his men out from the castle to meet the enemy, he gained early success, but unwisely pursued a retreating force, thus sacrificing the chance of overall victory. Meanwhile, de Montfort defeated the remainder of the royal army, led by the king's brother, and as a result Prince Edward was captured. The king was forced to sign the Mise of Lewes, accepting the Provisions of Oxford and putting de Montfort in a position of ultimate power, which would last until the Battle of Evesham.