In all the main army consisted of about 48,000 men of all arms; but this did not compose the whole of Wellington’s available resources. He had transferred a considerable detachment to the southern bank of the Tagus, to protect the Alemtejo against any possible descent by the French. It will be remembered that as early as the beginning of November[5] he had sent across the river Fane’s Portuguese cavalry and a battalion of Caçadores, who were directed to watch the road along the further bank, to prevent any trifling force of French from crossing in search of provisions, and to keep open the communications with Abrantes. As long as Masséna was threatening the Lines of Torres Vedras, there was no danger that he would throw anything more than a raiding party across the Tagus; he would want every man for the great assault. But when the Marshal gave up the offensive and retired to Santarem, the aspect of affairs was changed; it was quite possible that, with his army in a state of semi-starvation, he might venture to send a considerable detachment over the river, to gather the food which was so necessary to him. Nor was it unlikely that he might have a still more cogent reason for invading the Alemtejo. If, as Wellington thought probable[6], the army of Andalusia were to be ordered up to assist the army of Portugal, it would be of great importance for the latter to possess a footing on the left bank of the Tagus, as the communication with Soult’s troops must certainly be made in this direction. Accordingly there was good reason for securing the line of the river, and for cooping up Masséna in his limited sphere on its western bank. On the 19th-20th of November, Hill and the 2nd Division, attended as usual by Hamilton’s two Portuguese brigades, and with the 13th Light Dragoons attached, crossed the Tagus in boats a little to the north of Salvaterra, to reinforce Fane’s detachment. This was a serious force--10,000 men--which Wellington could ill spare, and he made elaborate arrangements to enable it to return in haste, in the event of Masséna’s once more taking the offensive on the western bank of the Tagus. The flotilla of gunboats and river craft, which had been guarding the river, was to be kept ready at Alhandra to bring back the 2nd Division, at the first alarm of a movement of the French from Santarem. Meanwhile Hill moved up the river and established his head quarters at Chamusca, a little north of Santarem, from which point he could both observe the main body of the French and impede any attempt that they might make to cross the river, and also could keep in touch with Abrantes, and reinforce it, supposing that Masséna showed any signs of molesting it. The British brigades of the 2nd Division were distributed along the river, William Stewart’s at Pinheiros and Tramagal most to the north, Hoghton’s at Chamusca, Lumley’s at Almeirim, exactly facing Santarem. Hamilton’s two Portuguese brigades