In order to understand the ensuing military movements, it will be proper for the reader to study the map of the valley, and acquaint himself fully with the relative posture of both parties. The plans of both generals in chief were well made; but the blunders and obstinacy of the Mexican second in command disconcerted Santa Anna's desired combination, and ultimately opened the ground to the American advance with more ease than was anticipated.

We will sketch rapidly the military value of the arena upon which the combatants stood on the 18th of August, 1847.

Let us imagine ourselves beside General Scott, standing on one of the elevations above the town of San Agustin de las Cuevas, at the base of the southern mountain barrier of the valley, and looking northward towards the capital. Directly in front, leading to the city, is the main road, the left or western side of which, even from the gate of San Agustin to the Hacienda of San Antonio, and thence westwardly to San Angel, forms, together with the bases of the southern and western mountains about St. Geronimo and Contreras, a vast basin, ten or twelve square miles in extent, covered with the Pedregal or the field of broken lava which we have already mentioned. This mass of jagged volcanic matter, we must remember, was at that time barely passable with difficulty for infantry, and altogether impassable for cavalry or artillery, save by a single mule path. North, beyond the fortified hacienda and headquarters of Santa Anna at San Antonio, the country opened. A line of field works, the lake of Xochimilco, a few cultivated farms, and vast flooded meadows, were on its right to the east, but from the hacienda, a road branches off to the west, leading around the northern edge of the Pedregal or lava field through Coyoacan and San Angel, whence it deflects southwardly to Contreras. The main road, however, continues onward, northwardly, from the hacienda of San Antonio, until it crosses the Churubusco river at the strong fortification we have described. Beyond Churubusco the highway leads straight to the gate of San Antonio Abad, whence a work had been thrown north-westwardly towards the citadel. The city of Mexico, built on the bed of an ancient lake, was on a perfect level, nor were there any commanding or protecting elevations of importance around it within two or three miles, and the first of these, beyond this limit, were chiefly on the north and west.

Thus, General Santa Anna, in front, on the main road to the city, at the massive fortified hacienda of San Antonio, blocked up the highway in that direction, protected on his right by the barrier of the Pedregal; and by the lake of Xochimilco, the field works, and the flooded country on his left. General Valencia had been placed by him with his troops at San Angel, on the western edge of the valley, and at the village of Coyoacan, a little further east in the lap of the valley, on roads communicating easily with his position at San Antonio, while they commanded the approaches to the city by the circuitous path of the Pedregal around the edge of the valley from San Agustin de las Cuevas, through Contreras or Padierna. Valencia and Santa Anna were consequently within supporting distance of each other; and in their rear, in front of the city, were the fortifications of Churubusco. General Scott, with the whole American army was, therefore, apparently hemmed in between the lakes and the Pedregal on his flanks; the Mexican fortifications and army in front; and the steep mountains towards Cuernavaca in his rear. He was obliged, accordingly, either to retreat by the defiles through which he had advanced from Chalco,—to climb the steeps behind him and pass them to the tierra caliente,—to force the position in front at the hacienda of San Antonio,—or to burst the barrier of the Pedregal on his left, and, sweeping round the rim of the valley, to advance towards the capital through the village of San Angel. Such were some of the dangers and difficulties that menaced Scott on his arrival at San Agustin. He was in the heart of the enemy's country, in front of a capital aroused by pride, patriotism and despair, and possessing all the advantages of an accurate knowledge of the ground on which it stood, or by which it was surrounded. Scott, on the other hand, like the mariner in storm on a lee shore, was obliged to feel his way along the dangerous coast with the lead, and could not advance with that perfect confidence which is ever the surest harbinger of success.

The reconnoissances of the American engineers which had been pushed boldly, in front, on the main road, to the north, by the hacienda of San Antonio, soon disclosed the difficulty in that direction. But among the mass of information which the American General received at Puebla, his engineers learned that there was a pathway through this Pedregal whose route had been indicated by the spies with sufficient distinctness and certainty to justify a hope that he might be able to render it practicable for his whole army, and, thus, enable him to turn the right flank of the Mexicans' strongest positions. There is no doubt, as subsequent events demonstrated, that the ground in the neighborhood of Contreras, where the road descends from the mountains and barrancas towards San Angel was of great importance to the Mexicans in the defence of the various modes of access to the city, and it is unquestionable that a strong post should have been placed in that quarter to cripple the American advance. It is stated by Mexican writers, that General Mendoza, with two members of his topographical corps had reconnoitred this route and pass, and pronounced it "absolutely indefensible." It is probable, therefore, that no general action, involving the fortunes of a division, or of a large mass of the Mexican army, should have been risked among the ravines between the mountains and the Pedregal near Contreras; yet we do not believe that it should have been left by Santa Anna without a force capable of making a staunch resistance.

We are now acquainted with the ground, and with the positions of the two armies. Scott's plan was to force a passage by either or both of the two adits to the levels of the valley in front of the city, while Santa Anna's, according to his manifesto dated subsequently on the 23d of August, was to have made a concerted retrograde movement with his troops, and to have staked the fortunes of the capital on a great battle, in which all his fresh, enthusiastic, and unharmed troops would have been brought into a general action against the comparatively small American army, upon an open ground where he would have had full opportunity to use and manoeuvre infantry, cavalry and artillery.

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.

Thus fell the two main keys of the valley, and thus did all the divisions of the American army at length reach the open and comparatively unobstructed plains of the valley.

Worth soon reunited his division on the main straight road to the capital, and was joined by General Pillow, who, advancing from Coyoacan to attack the rear of San Antonio, as we have already related, soon perceived that the hacienda had fallen, and immediately turned to the left, through a broken country of swamps and ditches, in order to share in the attack on Churubusco. And here, it was felt on all sides, that the last stand must be made by Mexico in front of her capital.

The hamlet or scattered houses of Churubusco, formed a strong military position on the borders of the stream which crosses the highway, and, besides the fortified and massive convent of San Pablo, it was guarded by a tÊte de pont with regular bastions and curtains at the head of a bridge over which the road passes from the hacienda of San Antonio to the city. The stream was a defence;—the nature of the adjacent country was a defence;—and here the fragments of the Mexican army,—cavalry, artillery and infantry, had been collected from every quarter,—panic stricken, it is true,—yet apparently resolved to contest the passage of the last outwork of importance in front of the garita of San Antonio Abad.

When Worth and Pillow reached this point, Twiggs had already been sometime hotly engaged in attacking the embattled convent. The two advancing Generals immediately began to manoeuvre closely upon the tÊte de pont, which was about four hundred and fifty yards east of the convent, where Twiggs still earnestly plied the enemy. Various brigades and regiments under Cadwallader, Lieutenant Colonel Smith, Garland, Clark, Major White and Lieutenant Colonel Scott continued to press onward towards the tÊte de pont, until by gradual encroachments under a tremendous fire, they attained a position which enabled them to assault and carry the formidable work by the bayonet. But the convent still held out. Twenty minutes after the tÊte de pont had been taken, and after a desperate battle of two hours and a half, that stronghold threw out the white flag. Yet it is probable that even then the conflict would not have ended, had not the 3d infantry under Captains Alexander, J. M. Smith, and Lieutenant O. L. Shepherd, cleared the way by fire and the bayonet to enter the work.

Whilst this gallant task was being performed in front of the Mexican defences, Generals Pierce and Shields had been engaged on our left, in turning the enemy's works so as to prevent the escape of the garrisons, and to oppose the extension of numerous corps from the rear, upon and around our left. By a winding march of a mile around to the right, this division under the command of Shields, found itself on the edge of an open, wet meadow, near the main road to the capital, in the presence of nearly four thousand of the enemy's infantry, a little in the rear of Churubusco. Shields posted his right at a strong edifice, and extended his left wing parallel to the road, to outflank the enemy towards the capital. But the Mexicans extended their right more rapidly, and were supported by several regiments of cavalry, on better ground. Shields, accordingly, concentrated his division about a hamlet, and attacked in front. The battle was long and bravely sustained with varied success, but finally resulted in crowning with victory the zeal and courage of the American commander and his gallant troops. Shields took 380 prisoners, including officers; while at Churubusco seven field pieces, some ammunition, one standard, three Generals, and 1261 prisoners, including other officers, were the fruits of the sharply contested victory.

This was the last conquest on that day of conquests. As soon as the tÊte de pont fell, Worth's and Pillow's divisions rushed onward by the highway towards the city, which now rose in full sight before them, at the distance of four miles. Bounding onward, flushed and exultant, they encountered Shields' division, now also victorious, and all combined in the headlong pursuit of the flying foe. At length the columns parted, and a small part of Harney's cavalry, led by Captain Kearney of the 1st dragoons, dashed to the front and charged the retreating Mexicans up to the very gates of the city.

Thus terminated the first series of American victories in the valley of Mexico.