The Anglo-Gascon force of 4,000–6,000 men marched from Bordeaux in English-held Gascony to Narbonne and back to Gascony, devastating a wide swathe of French territory and sacking many French towns on the way. While no territory was captured, enormous economic damage was done to France; the modern historian Clifford Rogers concluded that "the importance of the economic attrition of the "chevauchée" can hardly be exaggerated." The English component resumed the offensive after Christmas to great effect, and more than 50 French-held towns or fortifications were captured during the following four months. In August 1356 the Black Prince headed north on another devastating "chevauchée" with 6,000 men; he was intercepted by the main French army, 11,000 strong, and forced to battle at Poitiers, where he decisively defeated the French and captured King John II of France.