|Along the road to Mexico city, Scott encountered no further significant resistance. Santa Ana however was relying on the powerful fortification of the city to defeat Scott. President Polk wanted one last chance to reach a peace agreement with the Mexicans, but his overture was turned down. Santa Ana however claimed that if he received $10,000 now and $1,000,000 after the surrender he would do so. He was given the $10,000, but that was the last heard from him on the subject.
The way to Mexico City was through a group of causeways through marches to the east of the city. Santa Ana had heavily fortified these approaches. Once again Captain Lees reconnaissance was invaluable. He found an unguarded way through the marches which was partially under water, and the American army made its way through there. The Americans thus moved closer to the city. Santa Ana shorter lines of communication allowed Santa Ana to move men to block the American advance. General Valencia without orders from Santa Ana decided not to wait for the Americans and instead moved out with a force of 4,000 men to outflank the American forces. American forces then moved up on Valencia forces once again on a path discovered by Lee. The American engaged Valencia forces who fought fiercely. Santa Ana then appeared with 9,000 men. The Americans feared they would be attacked on two sides, but a sudden downpour convinced Santa Ana to withdraw. That night the American forces made their way towards Valencias lines at Conreras. In the morning they had reached the rear of his lines and assaulted there. The Americans routed the Mexicans. Those who were not killed or wounded withdrew quickly. The American followed the Mexicans to the next fortress- Churubusco, which they attacked without proper reconnaissance. The American forces made three costly and unsuccessful assaults on the fortress. Finally, American reinforcements arrived, and in a final assault managed to carry to fortifications. American forces followed the Mexican withdrawal to the wall of Mexico City itself. In two days of fighting Americans lost 139 dead and 876 wounded. The Mexican lost 4,000 killed and wounded plus 3,000 captured.
There were two more Mexican fortresses, The first Molino del Rey and it was quickly taken. The final fortress was Chapultepec. It was a well defended castle with outlying fortifications. The Americans made an all out assault on the fortress. Despite heavy losses the Americans carried the fortress. The next day the city surrendered.