Accordingly, to meet contingencies, Major-General Worth was ordered to leave early in the morning of the 20th, one of his brigades to mask San Antonio, and to march with the other six miles, via San Augustin, upon Contreras. A like destination was given to Major-General Quitman and his remaining brigade in San Augustin, replacing, for the moment, the garrison of that important depot with Harney's brigade of cavalry, as horse could not pass over the intervening lava, etc., to reach the field of battle.
A diversion for an earlier hour (daylight) had been arranged the night before, according to the suggestion of Brigadier-General P. F. Smith, received through the engineer, Captain Lee, who conveyed my orders to our troops remaining on the ground, opposite to the enemy's centre, a point for the diversion or the real attack, as circumstances might allow.
Guided by Captain Lee, it proved the latter, under the command of Colonel Ransom of the 9th, having with him that regiment and some companies of three others, the 3d, 12th, and Rifles.
Shields, the senior officer of the hamlet, having arrived in the night, after Smith had arranged with Cadwallader and Riley the plan of attack for the morning, delicately waived interference; but reserved to himself the double task of holding the hamlet with his two regiments (South Carolina and New York Volunteers) against ten times his numbers on the side of the city, including the slopes to his left, and in case the enemy's camp in his rear should be carried, to face about and cut off the flying enemy.
At three a.m., the great movement commenced on the rear of the enemy's camp, Riley leading, followed successively by Cadwallader's and Smith's brigades, the latter temporarily under the orders of Major Dimick of the 1st Artillery, the whole force being commanded by Smith, the senior in the general attack, and whose arrangements, skill and gallantry always challenge the highest admiration.
The march was rendered tedious by the darkness, rain, and mud; but about sunrise, Riley, conducted by Lieutenant Turner, Engineer, had reached an elevation behind the enemy, whence he precipitated his columns; stormed the intrenchments, planted his several colors upon them, and carried the work, all in seventeen minutes.
Conducted by Lieutenant Beauregard, Engineer, and Lieutenant Brooks of Twiggs' staff, both of whom, like Lieutenant Tower, had, in the night, twice reconnoitred the ground; Cadwallader brought up to the general assault two of the regiments: the Voltigeurs and the 11th, and at the appointed time Colonel Ransom, with his temporary brigade, conducted by Captain Lee, Engineer, not only made the movement in front, to divert and to distract the enemy, but, after crossing the deep ravine, advanced, and poured into the works and upon the fugitives many volleys from his destructive musketry.
In the mean time Smith's own brigade, under the temporary command of Major Dimick, following the movements of Riley and Cadwallader, discovered, opposite to, and outside of the works, a long line of Mexican cavalry, drawn up as a support. Dimick having at the head of the brigade the company of Sappers and Miners, under Lieutenant G. W. Smith, engineer, who had conducted the march, was ordered by Brigadier-General Smith to form his line, faced to the enemy, and in a charge against the flank, routed the cavalry.
Shields, too, by the wise disposition of his brigade and gallant activity, contributed much to the general results. He held masses of cavalry and infantry, supported by artillery, in check below him, and captured hundreds, with one general (Mendoza), of those who fled from above.
I doubt whether a more brilliant or decisive victory, taking into view ground, artificial defences, batteries, and the extreme disparity of numbers, without cavalry or artillery on our side, is to be found on record. Including all our corps directed against the intrenched camp, with Shields' brigade at the hamlet, we positively did not number over four thousand five hundred rank and file; and we knew by sight, and since, more certainly, by many captured documents and letters, that the enemy had actually engaged on the spot seven thousand men, with at least twelve thousand more hovering within sight and striking distance, both on the 19th and 20th. All, not killed or captured, now fled with precipitation.