The march upon the capital began August 7, and on the 13th the army was assembled 15 miles from that city at and in the vicinity of Ayotla. From this point three roads led to the city; and in exploring the most direct one, the Dragoons and Mounted Rifles, escorting General [Persifor F.] Smith and Engineers, took such liberties with the powerful and heavily garrisoned works of El Pe¤on and Mexicalcingo that General Scott pronounced this "the boldest reconnaissance of the war".

It was finally decided to advance by the road south of Lake Chalco to San Augustin, which place was seized August 17, and next day the entire army had arrived in that vicinity.

Within 5 miles of San Augustin were the strong posts of San Antonio and Contreras; the former on the direct road to the capital, very strong and nearly inaccessible excepting by way of a narrow causeway flanked by deep ditches; the latter on the treat road from Acapulco to Mexico, also very strong, well fortified, armed with 22 cannon and occupied by General Valencia with 7,000 veterans, said to be the flower of the Mexican army. It was decided to mask San Antonio and to attack Contreras.

A path having been made passable through the pedrigal or field of lava, the brigade of Gen. [Persifor F.] Smith was on August 19 directed against Contreras and drove in the enemy's cavalry, skirmishers and advanced posts, but did not attack the main work. Two light batteries, brought forward with great difficulty, were opened against the enemy's works, but after a severe contest they were silenced. Leaving the guns supported by several companies of infantry (later reinforced by two regiments of [Franklin] Pierce's brigade) before the works, General Smith moved the remainder of his brigade to the right upon San Geronimo, to cut Contreras off from the capital and also from communication with Santa Ana, who with 12,000 men had advanced to support Valencia, and who ultimately approached to within 2,000 yard of his works.

The brigade of General Smith was reinforced by those of Riley and [George] Cadwalader, and all three were at San Geronimo, interposed between Valencia and Santa Ana, before dark. The brigade of Shields was toiling through the pedrigal and joined the others during the night. The light batteries, having suffered severely, were withdrawn out of range. The situation at this time would seem to have called for immediate and vigorous action of some sort on the part of the enemy. It is asserted by some that the Mexicans did not know the movements of their enemy; but this would seem incredible. Be that as it may, General Valencia spent the precious moments in writing a very extravagant report of his "victory" and in "conferring brevets upon his officers."

Most of the night, which was rainy and very dark, was spent by the Engineer officers in searching for a possible route to the rear of the enemy's works. The movement began at 3 o'clock a.m. on the 20th, with Riley's brigade in the lead. The brigade of Shields remained at San Geronimo to withstand any movement of Santa Ana. The other three brigades did not finish their movement until long after daylight. Yet they remained undiscovered until they were almost ready to assault, the enemy's attention being more particularly devoted to the troops still occupying the first position, near Padierna.

At about 6:30 a.m. Valencia's position was assaulted in rear and on both flanks, and in a few minutes his entire force was utterly routed and "totally destroyed as a military body".

"I doubt whether a more brilliant or decisive victory--taking into view ground, artificial defenses, 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's brigade at the hamlet, we positively did not have over 4,500 rank and file, and we know by sight, and more certainly by many captured documents and letters, that the enemy had actually engaged on the spot 7,000 with at least 12,000 more hovering within sight and striking distance, both on the 19th and 20th.

"All not killed or captured now fled with precipitation. Thus was the great victory of Contreras achieved; our road to the capital opened; 700 of the enemy killed; 813 prisoners, including 88 officers, 4 generals, besides various colors and standards 22 pieces of brass ordnance, half of large caliber, thousands of small arms and accouterments, an immense quantity of shot and shell, powder and cartridges, 700 pack mules and many horses--all in our hands." [General Scott's Report.]

Two of these guns were Santa Ana's trophies from the field of Buena Vista. They had been "lost without dishonor" by a battery of 4th Artillery, Captain O'Brien, at Buena Vista. They were now "recovered with glory" by Capt. Simon Drum's battery of the same regiment.

The fortified post of San Antonio, the bridge head of Churubusco, and the fortified convent of San Pablo adjacent were all captured after hard fighting on the same day. While the battle of Churubusco was in progress the brigades of Shields and [Franklin] Pierce were sent by the commanding general to attack the Mexican reserves in rear of the lines of Churubusco. The resulting combat, called the "battle of Portales", was very severe for a time, but terminated in the fifth American victory on that memorable 20th of August.

"So terminated the series of events which I have but feebly presented. My thanks were freely poured out on the different field to the abilities and services of generals and other officers, to the zeal and prowess of all, the rank and file included. But a reward infinitely higher, the applause of a grateful country and Government, will, I can not doubt, be accorded in due time to such merit of every sort displayed by this glorious army, which has now overcome all difficulties, distance, climate, ground, fortifications, and numbers.

"It has in a single day in many battles as often defeated 32,000 men, made about 3,000 prisoners, including 8 generals, two of them ex-Presidents, and 205 other officers; killed and wounded 4,000 of all ranks, besides entire corps dispersed and dissolved; captured 37 pieces of ordnance, more than trebling our siege train and field batteries, with a large number of small arms and a full supply of ammunition of every kind. These great results have overwhelmed the enemy. Our loss amounts to 1,053; 139, including 16 officers, were killed; 876, with 60 officers were wounded.

"After so many victories, we might with but little additional loss have occupied the capital the same evening.

"I halted our victorious corps at the gates of the city, at least for a time, and have them now quartered."
[ibid.]

Negotiations were undertaken, but failed, and operations were resumed on the 7th of September. Next day occurred the battle of Molino del Rey, in which 3,250 Americans defeated 14,000 Mexicans, who occupied a very powerful line of works, flanked by the fire of the castle of Chapultepec. Four thousand lancers, the finest cavalry in the world, were completely bluffed and intimidated by Major Sumner with 270 dragoons, and they took no part in the battle except that of spectators. The enemy was driven from his works with heavy losses, including all his artillery and 800 prisoners; but, as at Buena Vista, Santa Ana proclaimed a great victory won by himself a "victory" the anniversary of which is celebrated in Mexico to this day.

After the destruction of the powerful stone works of Molino del Rey, including the Casa Mata Fort, there still remained between the American army and the capital only the Castle of Chapultepec. This renowned fortress was battered all day on September 12 and next morning was carried by assault. The Belen and San Cosmo causeways and gates were captured in the afternoon of the same day.

On September 14 the city was occupied with little opposition, and, although minor operations continued for a time, the war was practically at an end.