But this plan was disconcerted at first, and probably destroyed, both in its materiel and morale, by the gross disobedience of General Valencia, who forgot as a soldier, that there can never be two commanders in the field. Valencia, apparently resolving to seize the first opportunity to attack the Americans, in spite of the reported untenable character of the ground about Padierna or Contreras, left his quarters at Coyoacan and San Angel, and advanced, without consulting his commander, to Contreras, upon whose heights he threw up an entrenched camp! As soon as Santa Anna learned this fact, he ordered the vain and reckless officer to retire, but finding him obstinately resolute in his insubordination, the commander-in-chief suffered him, in direct opposition to his own opinion, to remain and to charge himself with the whole responsibility of the consequences. Thus, if Scott advanced upon the main road, he would meet only Santa Anna in front, and the efficiency of Valencia's force, on his left flank, would be comparatively destroyed. If he conquered Valencia, however, at Contreras, after passing the Pedregal, he would rout a whole division of the veterans of the north—the remnants of San Luis and Angostura,—while the remainder of the army, composed of recent levies and raw troops, disciplined for the occasion, would, in all likelihood, fall an easy prey to the eager Americans.
The reconnoissances of the American army were now completed both towards San Antonio over the main northern road, and towards Padierna or Contreras over the southern and south-western edge of the Pedregal. That brave and accomplished engineer, Captain—now Colonel Robert E. Lee—had done the work on the American left across the fields of broken lava, and being convinced that a road could be opened, if needed, for the whole army and its trains, Scott resolved forthwith to advance.
On the 19th of August, General Pillow's division was commanded to open the way, and advancing carefully, bravely and laboriously over the worst portion of the pass,—cutting its road as it moved onward,—it arrived about one o'clock in the afternoon at a point amid the ravines and barrancas near Padierna or Contreras where the new road could only be continued under the direct fire of twenty-two pieces of Mexican artillery, most of which were of large calibre. These guns were in a strong entrenched camp, surrounded by every advantage of ground and by large bodies of infantry and cavalry, reinforced from the city, over an excellent road beyond the volcanic field. Pillow's and Twiggs's force, with all its officers on foot, picking a way along the Mexican front and extending towards the road from the city and the enemy's left, advanced to dislodge the foe. Captain Magruder's field battery of twelve and six-pounders, and Lieut. Callender's battery of mountain howitzers and rockets, were also pushed forward with great difficulty within range of the Mexican fortifications, and, thus, a stationary battle raged until night fell drearily on the combatants amid a cold rain which descended in torrents. Wet, chilled, hungry and sleepless, both armies passed a weary time of watching until early the next morning, when a movement was made by the Americans which resulted in a total rout of Valencia's forces. Firing at a long distance against an entrenched camp was worse than useless on such a ground, and although General Smith's and Colonel Riley's brigades, supported by Generals Pierce's and Cadwallader's, had been under a heavy fire of artillery and musketry for more than three hours along the almost impassable ravine in front and to the left of the Mexican camp, yet so little had been effected in destroying the position that the main reliance for success was correctly judged to be in an assault at close quarters. The plan had been arranged in the night by Brigadier General Persifer F. Smith, and was sanctioned by General Scott, to whom it was communicated through the indefatigable diligence of Captain Lee, of the Engineers.
At 3 o'clock A. M. of the 20th August, the movement commenced on the rear of the enemy's camp, led by Colonel Riley and followed successively by Cadwallader's and Smith's brigades, the whole force being commanded by General Smith.
The march was rendered tedious by rain, mud and darkness; but, about sun rise, Riley reached an elevation behind the Mexicans, whence he threw his men upon the works, and, storming the entrenchments, planted his flag upon them in seventeen minutes. Meanwhile Cadwallader brought on the general assault by crossing the deep ravine in front and pouring into the work and upon the fugitives, frequent volleys of destructive musketry. Smith's own brigade under the temporary command of Major Dimick, discovered, opposite and outside the work, a long line of Mexican cavalry drawn up in support, and by a charge against the flank, routed the horse completely, while General Shields held masses of cavalry, supported by artillery, in check below him, and captured multitudes who fled from above.
It was a rapid and brilliant feat of arms. Scott,—the skilful and experienced General of the field,—doubts in his despatch whether a more brilliant or decisive victory is to be found on record, when the disparity of numbers, the nature of the ground, the artificial defences, and the fact that the Americans accomplished their end without artillery or cavalry, are duly and honestly considered. All our forces did not number more than 4,500 rank and file, while the Mexicans maintained, at least, six thousand on the field, and double that number in reserve under Santa Anna, who had advanced to support but probably seeing that it was not a spot for his theory of a general action, and that an American force intervened, declined aiding his disobedient officer. The Mexicans lost about 700 killed, 813 prisoners, including 4 Generals among 88 officers. Twenty-two pieces of brass ordnance, thousands of small arms and accoutrements, many colors and standards, large stores of ammunition, 700 pack mules, and numbers of horses fell into the hands of the victors.
The rage of Santa Anna against Valencia knew no bounds. He ordered him to be shot wherever found; but the defeated chief fled precipitately towards the west beyond the mountains, and for a long time lay in concealment until the storm of private and public indignation had passed. The effect of this battle, resulting in the loss of the veterans of the north, was disastrous not only in the city, but to the morale of the remaining troops of the main division under Santa Anna. It certainly demonstrated the importance of Padierna or Contreras as a military point of defence; but it unquestionably proved that the works designed to maintain it should have been differently planned and placed at a much earlier day, after mature deliberation by skilful engineers. The hasty decision and work of Valencia, made without preconcert or sanction of the General-in-chief, and in total violation of his order of battle, followed by the complete destruction of the entire division of the northern army, could only result in final disaster.
Whilst the battle of Contreras was raging early in the day, brigades from Worth's and Quitman's divisions had been advanced to support the combatants; but before they arrived on the field the post was captured, and they were, accordingly, ordered to return to their late positions. Worth, advanced from San Agustin, in front of San Antonio, was now in better position, for a road to the rear of the hacienda had been opened by forcing the pass of Contreras. Moving from Contreras or Padierna through San Angel and Coyoacan, Pillow's and Twiggs's divisions would speedily be able to attack it from the north, while Worth, advancing from the south, might unquestionably force the position. Accordingly while Pillow and Twiggs were advanced, General Scott reached Coyoacan, about two miles, by a cross road, in the rear of the hacienda of San Antonio. From Coyoacan he despatched Pillow to attack the rear of San Antonio, while a reconnoissance was made of Churubusco, on the main road, and an attack of the place ordered to be effected by Twiggs with one of his brigades and Captain Taylor's field battery.
General Pierce was next despatched, under the guidance of Captain Lee, by a road to the left, to attack the enemy's right and rear in order to favor the movement on the Convent of Churubusco and cut off retreat to the capital. And, finally, Shields, with the New York and South Carolina volunteers, was ordered to follow Pierce and to command the left wing. The battle now raged from the right to the left of our whole line. All the movements had been made with the greatest rapidity and enthusiasm. Not a moment was lost in pressing the victory after the fall of Contreras. Shouting Americans and rallying Mexicans were spread over every field. Every one was employed; and, in truth, there was ample work to do, for even the commander-in-chief of our forces was left without a reserve or an escort, and had to advance for safety close in Twiggs's rear.
Meanwhile, about an hour earlier, Worth, by a skilful and daring movement upon the enemy's front and right at the hacienda of San Antonio, had turned and forced that formidable point whose garrison no doubt was panic struck by the victory of Contreras. The enterprise was nobly achieved. Colonel Clarke's brigade, conducted by the engineers Mason and Hardcastle, found a practicable path through the Pedregal west of the road, and, by a wide sweep, came out upon the main causeway to the capital. At this point the three thousand men of the Mexican garrison at San Antonio, were met in retreat, and cut by Clarke in their very centre;—one portion being driven off towards Dolores on the right, and the other upon Churubusco in the direct line of the active operations of the Americans. Whilst this brave feat of out-flanking was performed, Colonel Garland, Major Galt, Colonel Belton, and Lieutenant Colonel Duncan advanced to the front attack of San Antonio, and rushing rapidly on the flying enemy, took one General prisoner, and seized a large quantity of public property, ammunition and the five deserted guns.