Headquarters of the army,
Tacubaya, near Mexico, September 11, 1847.

Sir: - I have heretofore reported that I had, Aug. 24th, concluded an armistice with President Santa Anna, which was promptly followed by meeting between Mr. Trist and Mexican commissioners appointed to treat of peace.

Negotiations were actively continued, with, as we understood, some prospect of a successful result up the 2d instant, when our commissioner handed in his ultimatum, (on boundaries,) and the negotiators adjourned to meet again on the 6th.

Some infractions of the truce, in respect to our supplies from the city, were earlier committed, followed by apologies, on the part of the enemy. Those vexations I was willing to put down to the imbecility of the government, and waived pointed demands of reparation while any hope remained of a satisfactory termination of the war. But on the 5th, and more fully on the 6th, I learned that as soon as the ultimatum had been considered in a general council of ministers and others, President Santa Anna, on the 4th or 5th, without giving me the slightest notice, actively recommended strengthening the military defences of the city, in gross violation of the 3d article of the armistice.

On that information, which has since received the fullest verification, I addressed to him my note of the 6th. His reply, dated the same day, received the next morning, was absolutely and notoriously false, both in recrimination and explanation. I enclose copies of both papers, and have had no subsequent correspondence with the enemy.

Being delayed by the terms of the armistice more than two weeks, we had now, late on the 7th, to begin to reconnoiter the different approaches to the city, within our reach, before I could lay down any definitive plan of attack.

The same afternoon a large body of the enemy was discovered hovering about the Molino del Rey, within a mile and a third of this village, where I am quartered with the general staff of Worth's division.

It might have been supposed that an attack upon us was intended; but knowing the great value to the enemy of those mills, (Molinos del Rey,) containing a cannon foundry, with a large deposite of powder in Casa Mata near them; and having heard, two days before, that many church bells had been sent out to be cast into guns, the enemy's movement was easily understood, and I resolved, at once, to drive him early the next morning, to seize the powder, and to destroy the foundry.

Another motive for this decision - leaving the general plan of attack upon the city for full reconnoissances - was, that we knew our recent captures had left the enemy not a fourth of the guns necessary to arm, all at the same time, the strong works of each of the eight city gates; and we could not cut the communication between the foundry and the capital without first taking the formidable castle on the heights of Chapultepec, which overlooked both and stood between.

For this difficult operation, we were not entirely ready and moreover we might altogether neglect the castle, if as we then hoped, our reconnoissances should prove that the distant southern approaches to the city were more eligible than this southwestern approach.

Hence the decision promptly taken, the execution of which was assigned to Brevet Major General Worth, whose division was reinforced with Cadwallader's brigade of Pillow's division, three squadrons of dragoons under Major Sumner, and some heavy guns of the siege train under Captain Huger of the ordnance, and Capt. Drum of the 4th artillery - two officers of the highest merit.

For the decisive and brilliant results, I beg to refer the report of the immediate commander - Major General Worth - in whose commendations of the gallant officers and men - dead and living - I heartily concur; having witnessed, but with little interference, their noble devotion to fame and to country.

The enemy having several times reinforced his line and the action soon becoming much more general than I had expected, I called up, from the distance of three miles, first Major General Pillow, with his remaining brigade, (Pierce's,) and next Riley's brigade of Twiggs' division - leaving his other brigade (Smith's) in observation at San Angel. Those corps approached with zeal and rapidity; but the battle was won just as Brigadier General Pierce reached the ground, and had interposed his corps between Garland's brigade (Worth's division) and the retreating enemy.

The accompanying report mentions, with just commendation, two of my volunteer aids - Major Kirby, paymaster, and Major Gaines, of the Kentucky volunteers, I also had the valuable services, on the same field, of several other officers of my staff, general and personal - Lieut. Col. Hitchcock; acting inspector general; Captain R. E. Lee, engineer; Capt. Irwin, chief quartermaster; Captain Grayson, chief commissary, Capt. H. L. Scott, acting assistant adjutant general; Lieut. Williams, aid de camp, and Lieut. Lay, military secretary.

I have the honor to be, sir, with high respect,

Your most obedient servant,
WINFIELD SCOTT.