They devastated the country to the suburbs of Rouen before leaving a swath of destruction, rapine and slaughter along the left bank of the Seine to Poissy, from Paris. Duke John of Normandy, Philip's oldest son and heir, had been in charge of France's main army, campaigning in the English occupied province of Gascony in south-west France; Philip ordered him north, to reinforce the army facing Edward. Meanwhile, the English had turned north and become trapped in territory which the French had denuded of food. They escaped by fighting their way across the Somme against a French blocking force. Two days later, on 26 August 1346, fighting on ground of their own choosing, the English inflicted a heavy defeat on the French at the Battle of Crécy.