If the French marshal had this admitted advantage on his side, in the possession of the line of the Douro, he had certainly other difficulties to embarrass him. The guerillas were in force on his flanks and in his rear, intercepting his convoys, and giving full occupation to a part of his corps that were required for a different service. These irregular bands were incessantly on the alert, crippling his resources, and cutting off stragglers and supplies. Sormel and Bombon were on his right; Julian Sanchez on the left; Porlier disturbed the country between him and the Asturias; and Mina and Duran infested Navarre and Aragon. No wonder that Marmont awaited Bonnet’s junction, with a portion of the army of the north, with great anxiety. It was effected safely, and the Duke of Ragusa was now numerically superior to his rival, the entire French _corps d’armée_, amounting to forty-seven thousand men. This increase of strength, when united to other considerations, induced Wellington to decide on falling back towards the frontier of Portugal. His military chest was nearly exhausted--supplies must be exacted, after the iniquitous system of the French, or the army subjected to privations; and the very difficulty he must have found in removing his wounded to the frontier, in the event of a hostile collision, would have been quite sufficient to deter a cautious general, and one so particular in attention to his troops when disabled, from courting a battle on the banks of the Douro. Marmont lost no time in concentrating between Toro and San Roman. He passed the river on the evening of the 16th, while Wellington moved the allies to Canizal and Fuente le Pena. This was, however, a feint on the French marshal’s part. At night he recrossed the Douro, made a rapid movement on Tordesillas, passed the river there, and early on the 18th reached the Trebancos, after marching forty miles. This movement was well designed and ably executed. By it Marmont had placed himself in direct communication with the army of the Centre, then moving from the capital to his support--while an advance to Castrejon, endangered Anson’s brigade of cavalry, and the fourth and light divisions. As morning broke, the outlying pickets in front of Castrejon were alarmed by a distant firing, which momently became louder and more sustained. Presently Bock’s brigade were observed retiring before the enemy’s dragoons and light artillery. The British retreated by scattered squadrons, and thus avoided the certain loss that a cannonade would occasion cavalry retiring in dense masses. The infantry fell back in perfect order--and though severely pressed by the French divisions, threatened by the dragoons, and occasionally under a fire of forty guns, reached the Guarena with trifling loss.[184]