During the year 1811 the French arms made considerable progress on the east side of Spain: this did not however give them any real additional advantage as against Wellington. They had more fortresses to garrison, more territory to occupy, and the Spanish armies went on causing much the same trouble to them as before. Moreover Napoleon's system of giving the various generals independent spheres of action, with no common control except his own, worked in Wellington's favour. If he made a threatening movement against Marmont, who commanded what was called the army of Portugal, occupying the basin of the upper Douro, or against Soult in Andalusia, neither marshal could order the other to assist him by a diversion. There was an obvious difference between combined action ordered by a chief who controlled the whole, and co-operation arranged between equals who had each his own separate ends in view. Napoleon should either have come to Spain in person—he was too far off in point of time to direct from Paris—or have given one marshal[71] command throughout the country. When towards the end of 1811 Wellington judged that the time was come for operations no longer merely defensive in purpose, he formed his plans to take advantage of this want of union among his enemies. It has been pointed out that the ways into Spain from Portugal are practically three: but the central one by the valley of the Tagus being ill suited for the movements of armies, there are but two really advantageous. That by the basin of the Douro is guarded at the frontier by two fortresses, Almeida and Ciudad Rodrigo; that by the Guadiana is guarded by Elvas and Badajos. Without possession of the pair of fortresses commanding one route or the other, invasion is scarcely feasible: with both pairs in his hands Wellington could choose, and he already held both Almeida and Elvas. Accordingly he resolved during the winter season, when the French would have serious difficulty in moving, to besiege first one and then the other of the Spanish border fortresses. He began with Ciudad Rodrigo, partly because it was the easier task to prepare for, as he had a battering-train in Almeida of which the French knew nothing (the guns were supposed to have been brought there to arm the fortress), partly because he then purposed to move against Soult if he succeeded in capturing Badajos. The preparations for the siege were very quietly made in Almeida, and on January 8, 1812, the first British troops appeared before Ciudad Rodrigo. That very evening a detached fort to the north of the town was suddenly stormed, which enabled the trenches to be begun much nearer to the walls than could otherwise have been done. Wellington had calculated that he should require twenty-four days, but the uncertainties were great, for besides the prospect of Marmont coming to its relief, there was always the risk that heavy rain might raise the river Agueda in flood prematurely, which would have stopped the siege