Outside and within the cross-fires of those gates, we found to the south other obstacles but little less formidable. All the approaches near the city are over elevated causeways, cut in many places (to oppose us), and flanked on both sides by ditches, also of unusual dimensions. The numerous cross-roads are flanked in like manner, having bridges at the intersections, recently broken. The meadows thus checkered are, moreover, in many spots, under water or marshy; for, it will be remembered, we were in the midst of the wet season, though with less rain than usual, and we could not wait for the fall of the neighboring lakes and the consequent drainage of the wet grounds at the edge of the city, the lowest in the whole basin.
After a close personal survey of the southern gates, covered by Pillow's division and Riley's brigade of Twiggs', with four times our numbers concentrated in our immediate front, I determined on the 11th to avoid that network of obstacles, and to seek, by a sudden diversion to the southwest and west, less unfavorable approaches.
To economize the lives of our gallant officers and men, as well as to ensure success, it became indispensable that this resolution should be long masked from the enemy; and again, that the new movement, when discovered, should be mistaken for a feint, and the old as indicating our true and ultimate point of attack.
Accordingly, on the spot, the 11th, I ordered Quitman's division from Coyoacan, to join Pillow, by daylight, before the southern gates, and then that the two major-generals, with their divisions, should, by night, proceed (two miles) to join me at Tacubaya, where I was quartered with Worth's division. Twiggs, with Riley's brigade and Captain Taylor's and Steptoe's field batteries, the latter of twelve-pounders, was left in front of those gates to manœuvre, to threaten, or to make false attacks, in order to occupy and deceive the enemy. Twiggs' other brigade (Smith's) was left at supporting distance, in the rear, at San Angel, till the morning of the 13th, and also to support our general depot at Miscoac. The stratagem against the south was admirably executed throughout the 12th and down to the afternoon of the 13th, when it was too late for the enemy to recover from the effects of his delusion.
The first step in the new movement was to carry Chapultepec, a natural and isolated mound of great elevation, strongly fortified at its base, on its acclivities and heights. Besides a numerous garrison, here was the military college of the republic, with a large number of sub-lieutenants and other students. Those works were within direct gun-shot of the village of Tacubaya, and, until carried, we could not approach the city on the west without making a circuit too wide and too hazardous.
In the course of the same night (that of the 11th) heavy batteries, within easy ranges, were established. No. 1, on our right, under the command of Captain Drum, 4th Artillery (relieved late next day, for some hours, by Lieutenant Andrews, of the 3d), and No. 2, commanded by Lieutenant Hagner, Ordnance, both supported by Pillow's division, were commanded, the former, by Captain Brooks and Lieutenant S. S. Anderson, 2d Artillery, alternately, and the latter by Lieutenant Stone, Ordnance. The batteries were traced by Captain Huger and Captain Lee, Engineer, and constructed by them with the able assistance of the young officers of those corps and the Artillery.
To prepare for an assault, it was foreseen that the play of the batteries might run into the second day; but recent captures had not only trebled our siege-pieces, but also our ammunition; and we knew that we should greatly augment both by carrying the place. I was, therefore, in no haste in ordering an assault before the works were well crippled by our missiles.
The bombardment and cannonade, under the direction of Captain Huger, were commenced early in the morning of the 12th. Before nightfall, which necessarily stopped our batteries, we had perceived that a good impression had been made on the castle and its outworks, and that a large body of the enemy had remained outside, towards the city, from an early hour to avoid our fire, and to be at hand on its cessation, in order to re-enforce the garrison against an assault. The same outside force was discovered the next morning, after our batteries had re-opened upon the castle, by which we again reduced its garrison to the minimum needed for the guns.
Pillow and Quitman had been in position since early in the night of the 11th. Major-General Worth was now ordered to hold his division in reserve, near the foundry, to support Pillow; and Brigadier-General Smith, of Twiggs' division, had just arrived with his brigade from Piedad (two miles), to support Quitman. Twiggs' guns, before the southern gates, again reminded us, as the day before, that he, with Riley's brigade, and Taylor's and Steptoe's batteries, was in activity, threatening the southern gates, and there holding a great part of the Mexican army on the defensive.
Worth's division furnished Pillow's attack with an assaulting party of some two hundred and fifty volunteer officers and men, under Captain McKenzie, of the 2d Artillery; and Twiggs' division supplied a similar one, commanded by Captain Casey, 2d Infantry, to Quitman. Each of these little columns was furnished with scaling ladders.