The Battle of Northampton was a battle in the Second Barons' War. In April 1264 an encounter took place, as part of the Baron's War wherein Henry III of England besieged Simon de Montfort's supporters who were holed in at Northampton Castle. De Montfort mounted a rear-guard rescue attempt but on April 6, 1264 the castle fell and De Montfort's son (another Simon) was captured by the King's forces.