For four days Wellington, although discovering that a retreat was in progress, was unable to ascertain by which line Massena was really retiring. As soon as this point was cleared up, he ordered Beresford to concentrate near Abrantes; while he himself followed the line the main body of the French army seemed to be taking. It was soon found that they were concentrating at Pombal, with the apparent intention of crossing the Mondego at Coimbra; whereby they would have obtained a fresh and formidable position behind the Mondego, with the rich and untouched country between that river and the Douro, upon which they could have subsisted for a long time. Therefore, calling back the troops that were already on the march to relieve Badajos, which had not yet surrendered, he advanced with all speed upon Pombal, his object being to force the French to take the line of retreat through Miranda for the frontier, and so to prevent him from crossing the Mondego. Ney commanded the rear guard, and carried out the operation with the same mixture of vigour, valour, and prudence with which he, afterwards, performed the same duty to the French army on its retreat from Moscow. He fought at Pombal and at Redinha, and that so strenuously that, had it not been for Trant, Wilson, and other partisans who defended all the fords and bridges, Massena would have been able to have crossed the Mondego. Wellington however turned, one by one, the positions occupied by Ney; and Massena, believing that the force at Coimbra was far stronger than it really was, changed his plans and took up a position at Cazal Nova. Here he left Ney and marched for Miranda but, although Ney covered the movement with admirable skill, disputing every ridge and post of vantage, the British pressed forward so hotly that Massena was obliged to destroy all his baggage and ammunition. Ney rashly remained on the east side of the river Cerra, in front of the village of Foz d'Aronce and, being attacked suddenly, was driven across the river with a loss of 500 men; many being drowned by missing the fords, and others crushed to death in the passage. However, Ney held the line of the river, blew up the bridge, and his division withdrew in good order. Massena tarnished the reputation, gained by the manner in which he had drawn off his army from its dangerous position, by the ruthless spirit with which the operation was conducted; covering his retreat by burning every village through which he passed, and even ordering the town of Leiria to be destroyed, although altogether out of the line he was following.