Growing bolder with success, he crossed the Aqueda and, marching round to the rear of Ciudad Rodrigo, cut off and destroyed convoys intended for that town, causing great alarm to the garrison. These were absolutely ignorant of the operations of Massena, for so active were the partisans, in the French rear, that no single messenger succeeded in getting through and, even when accompanied by strong escorts, the opposition encountered was so determined that the French were obliged to fall back, without having accomplished their purpose. Thus, then, the garrison at Ciudad Rodrigo were ignorant both of Massena's whereabouts, and of the nature of the force that had thrown itself in his rear. Several times, strong parties of troops were sent out. When these were composed of cavalry only, they were boldly met and driven in. When it was a mixed force of cavalry, infantry, and artillery, they searched in vain for the foe. So seriously alarmed and annoyed was the governor that 3000 troops were withdrawn, from Salamanca, to strengthen the garrison. In December Massena, having exhausted the country round, fell back to a very strong position at Santarem; and Terence withdrew his whole force, save those guarding the defiles, to the neighbourhood of Abrantes; so that he could either assist the force stationed there, should Massena retire up the Tagus; and prevent his messengers passing through the country between the river and the range of mountains, south of the Alva, by Castello Branco or Velha; posting strong parties to guard the fords of the Zezere. So thoroughly was the service of watching the frontier line carried out, that it was not until General Foy, himself, was sent off by Massena, that Napoleon was informed of the state of things. He was accompanied by a strong cavalry force and 4000 French infantry across the Zezere, and ravaged the country for a considerable distance. Before such strength, Terence was obliged to fall back. Foy was accompanied by his cavalry, until he had passed through Castello Branco; and was then able to ride, without further opposition, to Ciudad Rodrigo. Beresford was guarding the line of the Tagus, between the mouth of the Zezere and the point occupied on the opposite bank by Wellington, sending a portion of his force up the Zezere; and these harassed the French marauding parties, extending their devastations along the line of the Mondego.