Henry of Grosmont, Earl of Derby arrived in Gascony in August, and breaking with the previous policy of cautious advance, struck directly at the largest French concentration, at Bergerac. He surprised and defeated the French forces, under Bertrand I of L'Isle-Jourdain and Henri de Montigny. The French suffered heavy casualties and the loss of the town, a significant strategic setback. The battle and subsequent capture of Bergerac were major victories; the plunder from the defeated French army and from sacking the town was immense. Strategically, the Anglo-Gascon army had secured an important base for further operations. Politically, local lords who had been undecided in their allegiance had been shown that the English were again a force to be reckoned with in Gascony.