During this era, Mexico City was surrounded by marshes flanked by water-filled ditches. The only way to enter was through causeways that led to Garitas, or gates, where sentry boxes and a fortified structure were located to collect taxes on goods entering the city. The American troops took the western causeways which led to the garitas of Belén (on the southwest side of the city) and San Cosmé (on the west side, north of the Belén Gate), both which were guarded by Chapultepec. After the fall of the Castle at Chapultepec, the fortifications at the Belén and San Cosmé gates were the primary remaining points of resistance to the American force. This image shows the conflict from behind the Mexican lines, as opposed to most images of the War which were depicted from the American lines. It is believed the figure with the cocked hat, in front of the column left of center, is Gen. Andrés Terrés, who Santa Anna entrusted to defend the garita.