 In April the elder Simon de Montfort, in control of London, assembled his forces at St Albans and marched to relieve Northampton, which was under siege by the royalists, but was too late to prevent the town's capture by betrayal.He then moved into Kent and laid siege to the royal stronghold of Rochester Castle, but on hearing reports of a royal advance on London he withdrew most of his forces from the siege to confront this threat.King Henry, however, bypassed the capital and the rebel army and raised the siege of Rochester, before capturing Tonbridge and Winchelsea from the rebels.