On September 13, 1847 Major General Winfield Scott captured Mexico City after taking the Castle of Chapultepec the night before. Below is the entry from the Oxford Companion to American Military History about the battle.
“Chapultepec, Battle of, and Capture of Mexico City (1847).By 12 September 1847, the Mexican War was almost over; the Americans had been victorious in every major engagement, New Mexico had surrendered, U.S. forces had subdued Upper California, and Maj. Gen. Winfield Scott and 7,000 U.S. troops were camped outside Mexico City.
The Mexican capital was built in an ancient lake bed and could only be approached on raised causeways that passed through sizable gateways into the walled city. Just southwest of the city, on a 200-foot-high hill, the castle of Chapultepec commanded key causeways and was the site of a military college. Scott decided to storm Chapultepec first. On 12 September , in order to keep Mexican commander Gen. Antonio López de Santa Anna and his 15,000 troops unsure of his ultimate plans, Scott ordered part of his force to demonstrate south and southeast of the capital while his artillery began to hammer at Chapultepec. U.S. infantry attacked, scaling the rocky summit with ladders and pickaxes early the next morning. Within two hours, Scott’s troops had overrun the castle. Among the 1,000 defenders were 100 boy cadets who died defending their college and Mexican honor. “Los Niños” became Mexican national heroes.
From Chapultepec, some of the victorious U.S. soldiers swarmed onto the causeway leading to the gates at the southwest corner of Mexico City, and others attacked the gateway near the northwest corner. The soldiers and a battalion of U.S. Marines broke through the walls. Mexican resistance was fierce. When nightfall stopped the fighting for the day, U.S. troops were inside the Mexico City, but only barely. Luckily, Mexican authorities decided not to contest further the U.S. attempt to capture the city, and Santa Anna withdrew his army during the night. The next day, General Scott triumphantly entered the city. U.S. troops suffered over 860 casualties; Mexican losses are estimated to have been at least twice that many.
The capture of Mexico City did not immediately end the war. Santa Anna led his army eastward and helped lay siege to the U.S. garrison at Puebla, but within a month U.S. reinforcements had lifted the siege and the fighting was over.”
James M. McCaffrey