document,

Report No. 31.

HEADQUARTERS OF THE ARMY, SAN AUGUSTIN, ACAPULCO ROAD, NINE MILES FROM MEXICO, August 19, 1847. SIR:

Leaving a competent garrison in Puebla, this army advanced upon the capital, as follows : Twiggs's division, preceded by Harney's brigade of cavalry, the Tth ; Quitman's division of volunteers, with a small detachment of United States Marines, the 8th ; Worth's division, the 9th, and Pillow's division, the 10th all in this month. On the 8th, I overtook, and then continued with the leading division.

The corps were, at no time, beyond five hours, or supporting distance, apart ; and on descending into the basin of the capital (seventy-five miles from Puebla) they became more closely approximated about the head of Lake Chalco, with Lake Tescuco a little in front and to the right.

On the 12th and 13th, we pushed reconnaissances upon the Penon, an isolated mound (eight miles from Mexico) of great height, strongly fortified to the top (three tiers of works) and flooded around the base by the season of rain and sluices from the lakes. This mound close to the national road, commands the principal approach to the city from the east. No doubt it might have been carried, but at a great and disproportionate loss, and I was anxious to spare the lives of this gallant army for a general battle which I knew we had to win before capturing the city, or obtaining the great object of the campaign a just and honorable peace.

Another reconnaissance (which I also accompanied) was directed the (13th) upon Mexicalcingo, to the left of the Pen on, a village at a fortified bridge across the outlet or canal, leading from Lake Jochimilco to the capital five miles from the latter. It might have been easy (masking the Penon) to force this passage ; but on the other side of the bridge, we should have found ourselves four miles from this (SAN AUGUSTIN) road, on a narrow causeway, flanked on the right and left by water or boggy ground.

Those difficulties, closely viewed, threw me back upon the project, long entertained, of turning the strong eastern defences of the city, by passing around south of Lake Chalco and Jochimilco, at the foot of the hills and mountains, so as to reach this point (SAN AUGUSTIN), and hence to manoeuvre, on hard ground, though much broken, to the south and southwest of the capital, which has been more or less under our view, since the 10th instant.

Accordingly, by a sudden inversion Worth's division, with Harney's cavalry brigade, leading we marched on the 15th instant. Pillow's and Quitman's divisions followed closely, and then Twiggs's division, which was left till the next day at Ayotla, in order to threaten the Penon and Mexicalcingo, and to deceive the enemy as long as practicable.

Twiggs, on the 16th, marching from Ayotla toward Chalco (six miles), met a corps of more than double his numbers cavalry and infantry under General Valencia. Twiggs halted, deployed into line, and by a few rounds from Captain Taylor's field battery, dispersed the enemy, killing or wounding many men and horses. No other molestation has been experienced except a few random shots from guerilleros on the heights ; and the march of twenty-seven miles, over a route deemed impracticable by the enemy, is now accomplished by all the corps thanks to their indomitable zeal and physical energy.

Arriving here, the 18th, Worth's division and Harney's cavalry were pushed forward a league, to reconnoitre and to carry, or to mask, San Antonio on the direct road to the capital. This village was found strongly defended by field works, heavy guns, and a numerous garrison. It could only be turned by in fantry, to the left, over a field of volcanic stones and lava ; for, to our right, the ground was boggy.

It was soon ascertained by the daring engineers, Captain Mason and Lieutenants Stevens and Tower, that the point could only be approached by the front, over a narrow causeway, flanked with wet ditches of great depth. Worth was ordered not to attack, but to threaten and to mask the place.

The first shot fired from San Antonio (the 18th) killed Captain S. Thornton, 2d Dragoons, a gallant officer, who was covering the operations with his company.

The same day, a reconnaissance was commenced to the left of SAN AUGUSTIN, first over difficult grounds, and farther on, over the same field of volcanic matter which extends to the mountains, some five miles from San Antonio, toward Magdalena. This reconnaissance was continued to-day by Captain Lee, assisted by Lieutenants Beauregard and Tower, all of the Engineers ; who were joined in the afternoon by Major Smith of the same corps. Other divisions coming up, Pillow's was advanced to make a practicable road for heavy artillery, and Twiggs's thrown farther in front, to cover that operation ; for, by the partial reconnaissance of yesterday, Captain Lee discovered a large corps of observation in that direction, with a detachment of which his supports of cavalry and foot under Captain Kearny and Lieutenant-Colonel Griham, respectively, had a successful skirmish.

By three o clock this afternoon, the advanced divisions came to a point where the new road could only be continued under the direct fire of twenty-two pieces of the enemy's artillery (most of them of large calibre) placed in a strong intrenched camp to oppose our operations, and surrounded by every advantage of ground, besides immense bodies of cavalry and infantry hourly reenforced from the city, over an excellent road beyond the volcanic field, and consequently beyond the reach of our cavalry and artillery.

Arriving on the ground an hour later, I found that Pillow's and Twiggs's divisions had advanced to dislodge the enemy, picking their way (all officers on foot) along his front, and extending themselves toward the road from the city and the enemy's left. Captain Magruder's field battery, of 12 and 6-pounders, and Lieutenant Callender's battery of mountain howitzers and rockets, had also, with great difficulty, been advanced within range of the intrenched camp. These batteries, most gallantly served, suffered much in the course of the afternoon, from the enemy's superior weight of metal.

The battle, though mostly stationary, continued to rage vrith great violence until nightfall. Brevet Brigadier-General P. F. Smith's and Brevet Colonel Riley's brigades (Twiggs s division), supported by Brigadier-Generals Pierce's and Cadwallader's brigades (Pillow's division), were more than three hours under a heavy fire of artillery and musketry along the almost impassable ravine in front and to the left of the intrenched camp.

Besides the twenty-two pieces of artillery, the camp and ravine were defended closely by masses of infantry, and these again supported by clouds of cavalry at hand, hovering in view. Consequently no decided impression could be made by daylight on the enemy's most formidable position, because, independently of the difficulty of the ravine, our infantry, unaccompanied by cavalry and artillery, could not advance in column without being mowed down by the grape and canister of the batteries, nor advance in line without being ridden over by the enemy's numerous cavalry. All our corps, however, including Magruder's and Callender's light batteries, not only maintained the exposed positions early gained, but all attempted charges upon them, respectively particularly on Riley, twice closely engaged with cavalry in greatly superior numbers were repulsed and punished.

From an eminence, soon after arriving near the scene, I observed the church and hamlet of Contreras (or Ansalda) on the road leading up from the capital through the intrenched camp to Magdalena, and seeing, at the same time, the stream of reinforcements advancing by that road from the city, I ordered (through Major-General Pillow) Colonel Morgan with his regiment, the 15th, till then held in reserve by Pillow, to move forward and to occupy Contreras (or Ansalda) being persuaded, if occupied, it would arrest the enemy's reinforcements and ultimately decide the battle.

Hiley was already on the enemy's left, in advance of the hamlet. A few minutes later, Brigadier-General Shields with his volunteer brigade (New York and South Carolina regiments Quitman's division) coming up under my orders from SAN AUGUSTIN, I directed Shields to follow and sustain Morgan. These corps, over the extreme difficulties of ground partially covered with a low forest before described, reached Con treras, and found Cadwallader's brigade in position, observing the formidable movement from the capital, and much needing the timely reenforcement.

It was alrea iy dark, and the cold rain had begun to fall in torrents upon our unsheltered troops ; for the hamlet, though a strong defensive position, could only hold the wounded men, and, unfortunately, the new regiments have little or nothing to eat in their haversacks. Wet, hungry, and without the possibility of sleep ; all our gallant corps, I learn, are fall of confidence, and only wait for the last hour of darkness to gain the positions whence to storm and carry the enemy's works.

Of the seven officers despatched since about sun down, from my position opposite to the enemy's centre, and on this side of the volcanic field to communicate instructions to the hamlet not one has succeeded in getting through these difficulties increased by darkness. They have all returned. But the gallant and indefatigable Captain Lee, of the Engineers, who has been constantly with the operating forces, is (eleven o clock p. M.,) just in from Shields, Smith, Cadwallader, etc., to report as above, and to ask that a powerful diversion be made against the centre of the intrenched camp toward morning.

Brigadier-General Twiggs cut off as above, from the part of his division beyond the impracticable ground, and Captain Lee are gone, under my orders, to collect the forces remaining on this side with which to make that diversion at about five o clock in the morning.

And here I will end this report, commenced at its date, and in another, continue the narrative of the great events which now impend.

I have the honor to be, etc., etc.,

WINFIELD SCOTT.

HON. WM. L. MARCY, Secretary of War.