It rained all night, and the men lay in the mud without fires. At three in the morning (August 20th) the word was passed to march. Such pitchy darkness covered the face of the plain that Smith ordered every man to touch his front file as he marched. Now and then a flash of lightning lit up the narrow ravine; occasionally a straggling moonbeam pierced the clouds and shed an uncertain glimmer on the heights; but these flitting guides only served to make the darkness seem darker. The soldiers groped their way, stumbling over stones and brushwood, and did not gain the rear of the camp till day broke. Then Riley bade his men look to the priming of their guns and reload those which the rain had wet. With the first ray of daylight the firing had recommenced between the Mexican camp and Ransom’s corps stationed in front and Shields’ brigade at San Jeronimo. Almost at the same moment Riley began to ascend the height in the rear. Before he reached the crest, his engineers, who had gone forward to reconnoitre, came running back to say that his advance had been detected, that two guns were being pointed against him, and a body of infantry were sallying from the camp. The news braced the men’s nerves. They gained the ridge, and stood a tremendous volley from the Mexicans without flinching. Poor Hanson of the Seventh--a gallant officer and an excellent man--was shot down with many others; but the Mexicans had done their worst. With steady aim, the volley was returned; and ere the smoke rose a cheer rang through the ravine and Riley fell with a swoop on the intrenchments. With bayonet and butt of musket, the Second and Seventh drove the enemy from his guns, leaping into his camp and slaughtering all before them. Up rushed Smith’s own brigade on the left, driving a party of Mexicans before them, and charging with the bayonet straight at Torrejon’s cavalry, which was drawn up in order of battle. Defeat was marked on their faces. Valencia was nowhere to be found. Salas strove vainly to rouse his men to defend themselves with energy; Torrejon’s horse, smitten with panic, broke and fled at the advance of our infantry. Riley hurled the Mexicans from their camp after a struggle of a quarter of an hour; and as they rushed down the ravine their own cavalry rode over them, trampling down more men than the bayonet and ball had laid low. On the right, as they fled, Cadwalader’s brigade poured in a destructive volley; and Shields, throwing his party across the road, obstructed their retreat and compelled the fugitives to yield themselves prisoners of war; The only fight of any moment had taken place within the camp. There, for a few minutes, the Mexicans had fought desperately; two of our regimental colors had been shot down; but finally Anglo-Saxon bone and sinew had triumphed. To the delight of the assailants, the first prize of victory was the guns O’Brien had abandoned at Buena Vista, which were regained by his own regiment.