The arches supporting the aqueduct afforded protection for advancing troops as well as to those engaged defensively.

At points on the San Cosme road parapets were thrown across, with an embrasure for a single piece of artillery in each.

At the point where both road and aqueduct turn at right angles from north to east, there was not only one of these parapets supplied by one gun and infantry supports, but the houses to the north of the San Cosme road, facing south and commanding a view of the road back to Chapultepec, were covered with infantry, protected by parapets made of sandbags.

The roads leading to garitas (the gates) San Cosme and Belen, by which these aqueducts enter the city, were strongly intrenched.
Deep, wide ditches, filled with water, lined the sides of both roads.
Such were the defences of the City of Mexico in September, 1847, on the routes over which General Scott entered.
Prior to the Mexican war General Scott had been very partial to General Worth--indeed he continued so up to the close of hostilities--but, for some reason, Worth had become estranged from his chief.

Scott evidently took this coldness somewhat to heart.