On 8 September 1847, as US forces continued the drive to Mexico City, intelligence was received that a cannon foundry and a large supply of gunpowder was believed to be at Molino del Rey, 1,000 yards east of Chapultepec Castle. MAJ Edwin V. Sumner took 270 Riflemen to screen the American flank as the attack on Molino del Rey began. 4,000 Mexican cavalrymen were poised to attack the US flank, but Sumner's men navigated a deep ravine (considered impassable by the Mexican cavalry), charged, and defeated the vastly superior force.