The capture of Calais in 1347 was followed by a truce, which, largely on account of the frightful ravages of the Black Death in both countries, was renewed again and again. In 1350 Philip VI. died, and was succeeded by his son John, who continued his father's policy. Year after year there were acts of hostility, chiefly but by no means exclusively on the French side, and abortive negotiations for peace. Edward offered repeatedly to resign his claims to the French crown on terms, but the price he asked was larger than the king of France could be expected to pay. At length in 1355 Edward was led by offered co-operation from the king of Navarre, which however came to nothing, to invade France in earnest once more. Two subsidiary expeditions were foiled by the winds, but the main one was carried out, and led to the great victory of Poitiers. The Black Prince, who commanded it, and who thenceforth was his father's representative in France, led a successful plundering expedition from Bordeaux across the south of France, but avoided serious fighting. Early in July the next year the prince started for a similar expedition on a larger scale, striking this time into the very heart of France. Two or three weeks earlier, the duke of Lancaster had left Brittany to unite with some Norman nobles who had risen in rebellion: and it is supposed by some writers that the two invasions were parts of a concerted scheme, by which the English hoped finally to conquer France. The direction of the Black Prince's march, the leisurely character of his proceedings, and the amount of plunder carried off, make this view highly improbable. Ignorance of topography, and the necessity of avoiding strong places which could not be captured, might account for some deviations from the straight route; the necessity of living on the country might account for the loss of a few days. It is not impossible that, aiming merely at the Loire, he should have gone as far east as Vierzon, instead of taking the direct route by Poitiers to Tours. But it is incredible that with such an object in view he should have consumed about three times the number of days necessary for covering the distance, or that he should have deliberately burdened his march with vast quantities of plunder. The prince was certainly a competent soldier for his age: and all accounts agree that his army was thoroughly under control, and that the plundering was systematic. He doubtless knew of his cousin's enterprise: but that there was intended to be real co-operation between them could only be believed on very good and positive evidence, which does not exist.