Owing to a circumstance of which Wellington could have no knowledge, the moment which he chose for his advance was even more propitious than he guessed. He knew of the march of Montbrun towards Valencia, and had made it the determining factor in his operations. But he was not, and could not be, aware of another fact of high importance. On December 29th Marmont, then at Talavera, had received a dispatch from Paris, dated on the 13th of the same month, informing him that the Emperor had resolved on making a sweeping change with regard to the respective duties and stations of the Armies of the North and of Portugal. Hitherto Dorsenne had been in charge of the whole kingdom of Leon: the troops stationed in it belonged to his army, and on him depended the garrisons of Ciudad Rodrigo, Astorga, and its other fortresses. He was, therefore, responsible for the keeping back of Wellington from all the ground north of the Sierra de Gata. Marmont, with his Army of Portugal, had to ‘contain’ the Anglo-Portuguese army south of that range, and had charge of the valley of the Tagus--northern Estremadura and those parts of New Castile which had been taken away from King Joseph’s direct control. From this central position the Duke of Ragusa had hitherto been supposed to be able to stretch out a hand to Dorsenne, in case of Wellington’s making a move in the valley of the Douro, to Soult in case of his showing himself opposite Badajoz. This indeed Marmont had done: he had brought up his army to Dorsenne’s aid in September, at the time of El Bodon and Aldea da Ponte: he had carried it down to the Guadiana and assisted Soult to relieve Badajoz in June.