The Battle of Lewes was one of two main battles 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".

The battle occurred because of the vacillation of King Henry III, who was refusing to honour the terms of the Provisions of Oxford, an agreement he had signed with his barons, led by Montfort, in 1258. The King was 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 500 yards to the north. A night march enabled Montfort's forces to surprise Prince 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.

The royalist army, perhaps as much as twice the size of Montfort's, was led by Edward on the right and the King's brother Richard of Cornwall on the left, while the King himself commanded the central battalion. Having led his men out from the castle to meet the enemy, Edward gained early success, but unwisely pursued a retreating force to the north, thus sacrificing the chance of overall victory. Meanwhile, Montfort defeated the remainder of the royal army led by the King and Cornwall. On being defeated, Cornwall decided to take refuge in the Priory. He was unable to reach the Priory so he hid in a windmill, where, upon his discovery, he was taunted with cries of "Come down, come down, thou wicked miller!" All three royals were eventually captured, and by imprisoning the King, Montfort became the de facto ruler of England.

Coordinates: 50°52′32″N 0°01′04″E / 50.875627°N 0.017855°E / 50.875627; 0.017855

Lewes ( /ˈluːɨs/) is the county town of East Sussex, England and historically of all of Sussex. It is a civil parish and is the centre of the Lewes local government district. The settlement has a history as a bridging point and as a market town, and today as a communications hub and tourist-oriented town. At the 2001 census it had a population of 15,988.

Archaeological evidence points to prehistoric dwellers in the area. Scholars think that the Roman settlement of Mutuantonis was here, as quantities of artifacts have been discovered in the area. The Saxons built a castle, having first constructed its motte as a defensive point over the river; they gave the town its name.

After the Norman invasion, William the Conqueror gave Lewes to William de Warenne, 1st Earl of Surrey. He built Lewes Castle on the Saxon site; and he and his wife, Gundred also founded the Priory of St Pancras, a Cluniac priory, in about 1081. Lewes was the site of a mint during the Late Anglo-Saxon period and thereafter a mint during the early years after the Norman invasion. In 1148 the town was granted a charter by King Stephen. The town became a port with docks along the Ouse River.