On the 21st, the allies being on San Christoval, the French threw a garrison into Alba de Tormes, from whence the Spaniards had been withdrawn by Carlos España, without the knowledge of the English general. Marmont then passed the Tormes by the fords, between Alba and Huerta, and moving up the valley of the Machechuco encamped at the outer edge of a forest. Wellington also passed the Tormes in the evening by the bridge of Salamanca and the fords of Santa Marta and Aldea Lengua; but the third division and D’Urban’s cavalry remaining on the right bank, intrenched themselves, lest the French, who had left a division on the heights of Babila Fuente, should recross the Tonnes in the night and overwhelm them. When the light division descended the rough side of the Aldea Lengua mountain to cross the river night had come down suddenly, and with more than common darkness, for a storm, that usual precursor of a battle in the Peninsula, was at hand. Torrents of rain deepened the ford, the water foamed and dashed with increasing violence, the thunder was frequent and deafening, and the lightning passed in sheets of fire close over the column, playing upon the points of the bayonets. One flash falling amongst the cavalry near Santa Marta killed many men and horses, while hundreds of frightened animals, breaking loose and galloping wildly about, were supposed to be the enemy charging in the darkness, and some of their patrols were indeed at hand, hovering like birds of prey: but nothing could disturb the beautiful order in which the serene veterans of the light division were seen by the fiery gleams to pass the foaming river, pursuing their march amidst this astounding turmoil, alike regardless of the storm and the enemy. The position now taken was nearly the same as that occupied by General Graham a month before, when the forts of Salamanca were invested. The left wing rested in low ground on the Tormes, having a cavalry post in front. The right wing was extended on a range of heights, which ended also in low ground, near the village of Arapiles: this line, perpendicular to the Tormes from Huerta to Salamanca, was parallel to it from Alba to Huerta, and covered Salamanca. Meanwhile the enemy, extending his left along the edge of the forest, menaced the line of communication with Rodrigo; and in the night advice came that General Chauvel, bringing up Caffarelli’s horsemen and twenty guns, had reached Pollos the 20th, and would join Marmont the 22nd or 23rd. Hence Wellington, feeling he must now retreat to Rodrigo, and fearing the French cavalry thus reinforced would hamper his movements, determined, unless they attacked him or committed some flagrant fault, to retire before Chauvel’s horsemen could arrive.