 The Dictum of Kenilworth , issued 31 October 1266 , was a pronouncement designed to reconcile the rebels of the Barons ' War with the royal government of England . After the baronial victory at the Battle of Lewes in 1264 , Simon de Montfort took control of royal government , but at the Battle of Evesham the next year Montfort was killed , and King Henry III restored to power . A group of rebels held out in the stronghold of Kenilworth Castle , however , and their resistance proved hard to crush . 
