Lancaster's strategy, in the early years of the renewed war, consisted mainly of attempts to wear down the force of France by devastating raids; he hoped to provoke the enemy to battle by striking at the heart of his realm, but never achieved his purpose. Warned by the disasters of Creçy and Poitiers, Charles V. and his great captain Bertrand du Guesclin would never commit themselves to an engagement in the open field. They let the English invaders pass by, garrisoning the towns but abandoning the countryside. Since Lancaster, in his great circular raids, had never the leisure to sit down to a siege--generally a matter of long months in the 14th century--he repeatedly crossed France leaving a train of ruined villages behind him, but having accomplished nothing else save the exhaustion of his own army. For the French always followed him at a cautious distance, cutting off his stragglers, and restricting the area of his ravages by keeping flying columns all around his path. But while the duke was executing useless marches across France, the outlying lands of Aquitaine were falling away, one after the other, to the enemy. The limit of the territory which still remained loyal was ever shrinking, and what was once lost was hardly ever regained. Almost the only reconquest made was that of the city of Limoges, which was stormed in September 1370 by the troops of the Black Prince, who rose from his sick-bed to strike his last blow at the rebels. His success did almost as much harm as good to his cause, for the deliberate sack of the city was carried out with such ruthless severity that it roused wild wrath rather than terror in the neighbouring regions. Next spring the prince returned to England, feeling himself physically unable to administer or defend his duchy any longer. English reverses. The greater part of Poitou, Quercy and Rouergue had been lost, and the English cause was everywhere losing ground, when a new danger was developed. Since Sluys the enemy had never disputed the command of the seas; but in 1372 a Spanish fleet joined the French, and destroyed off La Rochelle a squadron which was bringing reinforcements for Guienne. The disaster was the direct result of the campaign of Najera--for Henry of Trastamara, who had long since dethroned and slain his brother Peter the Cruel, remained a consistent foe of England. From this date onward Franco-Spanish fleets were perpetually to be met not only in the Bay of Biscay but in the Channel; they made the voyage to Bordeaux unsafe, and often executed descents on the shores of Kent, Sussex, Devon and Cornwall. It was to no effect that, in the year after the battle of La Rochelle, Lancaster carried out the last, the most expensive, and the most fruitless of his great raids across France. He marched from Calais to Bordeaux, inflicted great misery on Picardy, Champagne and Berry, and left half his army dead by the way.