Background

The Second Barons' War began in April of 1264 after Pope Urban IV absolved Henry III from his oath to observe the Provisions of Oxford, which were designed to ensure the King adhered to the rule of law and governed according to advice from his Barons.

By May, royalist forces under King Henry III had reached Lewes. King Henry III was encamped at St. Pancras Priory with a force of infantry, while his son, Prince Edward, was encamped at Lewes Castle with the cavalry, some 500 yards to the north.

Simon de Montfort, 6th Earl of Leicester approached the King to negotiate a truce, which the King rejected. De Montfort then orchestrated a night march from Fletching to Offham Hill, surprising the royalists and making camp for the night.

The baronial forces under de Montfort, despite being outnumbered, held the higher ground. Their bravery was symbolized by the white crosses they wore to distinguish themselves from the royalists.

Battle

Simon de Montfort demonstrated his strategic prowess by dividing his forces into four parts. His son, Henry de Montfort, along with Humphrey de Bohun and John de Burgh, was entrusted with one quarter. Another quarter was under the command of Gilbert de Clare, with John FitzJohn and William of Montchensy. The third quarter, comprising Londoners, was led by Nicholas de Segrave. Simon de Montfort himself led the fourth quarter, strategically held in reserve, with Thomas of Pelveston.

The royalist forces consisted of Henry III commanding the center, with Prince Edward, William de Valence, 1st Earl of Pembroke, and John de Warenne, 6th Earl of Surrey, on his right. Richard, the King's brother and 1st Earl of Cornwall, and his son, Henry of Almain, commanding the King's left flank.

The Battle of Lewes was initiated with a bold move by the baronial forces. They launched a surprise attack at dawn, catching the royalist foragers off guard as they were out gathering provisions. The battle unfolded with Prince Edward leading a cavalry charge against Segrave's Londoners, causing them to flee to the village of Offham. This left the King unsupported by cavalry, forcing him to launch an attack with his center forces straight up Offham Hill. Richard of Cornwall's men faltered, but Henry's men fought on until de Montfort's men arrived and forced the King to retreat.

The King's men were forced down the hill into Lewes, where they engaged in a fighting retreat to Lewes Castle and the priory. The King's horse was killed from under him, and he was captured. Richard, Earl of Cornwall, took refuge in a windmill as the battle rolled past him.

Following the battle, Edward returned with his cavalry and launched a counterattack. However, with the town ablaze and many of the King's supporters having fled, the battle had clearly shifted in favor of the Barons. This, coupled with the capture of the King, led Edward to accept de Montfort's offer of negotiations.

Aftermath

The King was forced to sign the Mise of Lewes, which has been lost to history. Henry was also forced to accept the Provisions of Oxford. Prince Edward remained a hostage of the Barons for almost a year. Several other royalist noblemen were taken prisoner, including Richard of Cornwall, Roger Mortimer, and Humphrey de Bohun.

Simon de Montfort was now in a position of ultimate power, which would last until Prince Edward's eventual escape and de Montfort's defeat at the Battle of Evesham.