two regiments (New York, and Palmetto, South Carolina) was ordered forward as a support.  General Persifor F. Smith now moved to the front across the pedregal, having left detachments as supports to the artillery of Magruder and Callender, which were ordered to open fire on the beginning of General Smith’s movement.  This movement of General Persifor F. Smith was led and conducted by Lieutenant Gustavus W. Smith.  When this force reached the village or town of San Geronimo a large force of the enemy came in sight.  Pierce’s brigade was at once ordered to the front, and was met by a heavy fire.  General Pierce having been disabled, Colonel Robert Ransom, of the Ninth Infantry, was in command of the forces, which were conducted by Lieutenant Isaac Ingles Stevens, and moved to the right and front of Magruder’s battery.  Ransom, uniting with the detachment left by General Smith, took possession of Padierna, driving the Mexican General Mendoza.  Riley’s command was the first to pass the pedregal, when it occupied the road on the opposite side with Captain Simon Henry Drum’s company of the Fourth Artillery.  A detachment of Mexican lancers escorting a train was encountered and captured.

Riley’s command continued its advance, when a company of Mexican lancers was met and repulsed by Captain Silas Casey’s company.  A mounted force, under the Mexican General Frontera, consisting of two regiments, was met and repulsed by the Second Infantry under Captain Charles T. Morris and the Seventh Infantry under Lieutenant-Colonel Joseph Plympton.  General Frontera was killed while leading a charge.  Riley now withdrew to San Geronimo, which he found occupied by Cadwallader’s and Smith’s brigades, and a regiment of Pierce’s brigade under command of Colonel George Washington Morgan.  When General Valencia’s advanced forces were driven in by Twiggs’s division on the pedregal, Valencia announced (August 19th, 2 P.M.) to General Santa Anna at San Antonio that the enemy were approaching Padierna, the artillery had opened fire, and the battle had begun.  General Santa Anna at once, on receipt of this information, sent an officer to Coyoacan with orders to General Perez to move at once to Padierna, and himself with two regiments and five pieces of artillery proceeded to join him.  He arrived at Coyoacan just at the time when the command of Perez was moving, and he ordered it to move rapidly.

On the evening of August 19th General P.F.  Smith was in San Geronimo with three brigades of infantry, but without cavalry or artillery.  His communications with the main army were cut off except through the pedregal.  He determined to attack, however, the next morning at daylight, carry the enemy’s works, and establish his communications with the main army.  His disposition of troops was as follows for the night:  Cadwallader’s command in the outer edge of the village of San Geronimo, Riley’s brigade parallel to it, the Rifles on the right, and