An hour or more before sunset we reached the top of the house above referred to. From that position the inside of the enemy's works could be plainly seen almost to the foot of the interior slope of the parapet. Our first fire upon the Mexicans, who were unconscious of the impending peril, was very deadly. Those who were not killed or disabled by that fire seemed dazed for an instant; but in a few moments, they precipitately retreated, leaving the San Cosme Garita without a single defender in the works. One of their pieces of artillery was withdrawn a few hundred yards, but was then abandoned.
Immediately after that first fire, a portion of the force with me on the roof became engaged with the enemy who appeared on house tops in rear of their battery. We soon drove them from their position. The other portion of our men fell back to the stairs, made their way to the lower story, broke open the thick, heavily barred, strong door, passed into the street, entered the abandoned works, and pursued the enemy. In the meantime, some of our troops from the right of the causeway had come forward and, a very small number of them, were slightly in advance of us in reaching the abandoned battery.
Colonel Garland, commander of the first brigade of Worth's division, on the right of the causeway, says, in his official report: "The enemy then took position at the Garita San Cosme, where they were supported by two pieces of artillery which raked the streets with grape and canister. Finding a secure position to the right of the second defence, [about 350 yards in front of the Garita], I reorganized the command as it came up; mounted a howitzer on the top of a convent, which, under the direction of Lieutenant [U. S.] Grant, Quartermaster, 4th Infantry, and Lieutenant Lendrum, 3rd Artillery, annoyed the enemy considerably. About this time, report was made to me that considerable progress had been made by the troops on the other side of the street by means of crowbars and pickaxes, working through houses and yards. This caused me to watch closely for the first movement of the enemy indicative of retreat. The moment this was discovered, the 4th Infantry, followed by detachments of the 2nd and 3rd Artillery, under Colonel Belton, rushed up the road, when they entered the work simultaneously with the forces operating to the right and left, Captain McKenzie's storming party slightly in advance". (Ex. Doc. No. 1, Appendix, p. 170.)