Sir: I have heretofore reported that I had, August 24, concluded an armistice with President Santa Anna, which was promptly followed by meetings between Mr. Trist and Mexican commissioners appointed to treat of peace.
Negotiations were actively continued with, as was understood, some prospect of a successful result, up to 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. These vexations I was willing to put down to the imbecility of the government, and waived any pointed demands of reparation while any hope remained of a satisfactory termination of the war. But on the 5th, and more fully on the sixth, I learned that as soon as the ultimatum had been considered in a grand council of ministers and others, President Santa Anna on the 4th or 5th, without giving me the slightest notice, actively recommenced 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 reconnoitre 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 Molinos del Rey, within a mile and a third of this village, where I am quartered with the general staff and 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 deposit of powder in Casa Mata near them, and having heard two days before that many church bells had been sent to be cast into guns, the 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 reconnoissance, 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 at 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 one.
Hence the decision promptly taken, the execution of which was assigned to Brevet Major-General Worth, whose division was re-enforced 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 Captain Drum of the 4th Artillery, two officers of the highest merit.