Grosmont, now known as Lancaster rather than Derby after the death of his father, sent an urgent appeal for help to Edward. Edward was not only morally obliged to succour his vassal, but also contractually required to; his indenture with Lancaster stated that if Lancaster were attacked by overwhelming numbers, then Edward "shall rescue him in one way or another". The garrison of Aiguillon, some 900 men, sortied repeatedly to interrupt the French operations, while Lancaster concentrated the main Anglo-Gascon force at La Réole, some away, as a threat. Duke John was never able to fully blockade the town, and found that his own supply lines were seriously harassed. On one occasion Grosmont used his main force to escort a large supply train into the town. In July the main English army landed in northern France and moved towards Paris. Philip VI repeatedly ordered his son, Duke John, to break off the siege and bring his army north. Duke John, considering it a matter of honour, refused. By August, the French supply system had broken down, there was a dysentery epidemic in their camp, desertion was rife and Philip's orders were becoming imperious. On 20 August the French abandoned the siege and their camp and marched away. Six days later the main French army was decisively beaten in the Battle of Crécy with very heavy losses, before Duke John's army could reinforce them. The English then laid siege to the port of Calais. Philip vacillated: on the day the siege of Calais began he disbanded most of his army, to save money and was convinced that Edward had finished his chevauchée (large-scale mounted raid) and would proceed to Flanders to ship his army home. On or shortly after 7September, Duke John made contact with Philip, having shortly before disbanded his own army. On 9September Philip announced that the army would reassemble at Compiègne on 1October, an impossibly short interval, and then march to the relief of Calais. Among other consequences, this equivocation allowed Grosmont in the south-west to launch offensives into Quercy and the Bazadais; and himself lead a chevauchée north through Saintonge, Aunis and Poitou, capturing numerous towns, castles and smaller fortified places and storming the rich city of Poitiers. These offensives completely disrupted the French defences in the region and shifted the focus of the fighting from the heart of Gascony to or more beyond its borders. Few