The American army having thus captured the fortifications of the capital of the enemy's country, a magnificent city of nearly 200,000 inhabitants, a secure lodgement was immediately effected in large houses, on the left of the street, a few hundred yards from the Garita. I then proceeded, with the engineer company and an infantry detachment, several hundred yards farther; and found a strong position, on the right of the street where the troops could rest protected from fire. Going farther to the front, I discovered that, 150 yards in advance there was a large convent, on the left of the street, occupied by a strong force. The next cross street, the Paseo, had batteries upon it. These facts were reported to General Worth, who ordered forward two brigades--one to occupy each of the positions selected--and, directed me to place those troops, station the picket-guards, and then, with Lieutenant McClellan, report at his headquarters which was several hundred yards within the Garita. The aqueduct, in the middle of the street along which we advanced, was an open stone trough, supported at a height of ten feet, or more, by pillars and arches. There was a good deal of firing down the street from Mexican detachments; but, by taking shelter under the arches, between the pillars, our men, in small groups, were quite well protected. A little before dark, whilst I was under one of the arches at the extreme front, endeavoring to get a closer view of the enemy at the convent and on the Paseo, I was joined by Lieutenant Sydney Smith, of the Fourth Infantry, who had borne several messages from me to General Worth during the afternoon. In a few moments after he joined me we heard horses feet rapidly approaching us from the direction of the citadel. These horsemen were captured, and proved to be three Mexican officers, one of whom was Adjutant-General on the staff of Santa Anna.