The city's defences were antiquated and derelict, but the size of the French force defending it prohibited an assault. Derby blockaded Périgueux and captured strongholds blocking the main routes into the city. John, Duke of Normandy, the son and heir of Philip VI, gathered an army reportedly numbering over 20,000 and manoeuvred in the area. In early October a very large detachment relieved the city and drove off Derby's force, which withdrew towards Bordeaux. Further reinforced, the French started besieging the English-held strongpoints.