The term of enlistment of 4000 twelve-months Volunteers being almost expired, he waits in Puebla for reinforcements.
August 7 he resumes the march for the Mexican capital, ninety-five miles. His force numbers 10,800, and he needs must cut loose from communications with Vera Cruz, his base.
August 9, from Rio Frio Pass, elevation 10,000 feet, on the summit of the main mountain range of Mexico, the army gazes down into the Valley of Mexico, with the city of Mexico visible, thirty-five miles distant.
By a new and difficult route he avoids the defences of the main road to the city, and on August 18 has approached to within nine miles and striking distance of the outer circle of batteries.
August 19–20, by day and night attack, 3500 Americans carry the strong entrenchments of Contreras defended by 7000 Mexicans. American loss, in killed and wounded, 60; Mexican casualties, 700 killed, 1000 wounded.
The same day, August 20, 1847, the outpost of San Antonio is taken, the high citadel of Churubusco stormed. There are five separate actions, all victorious, and the dragoons charge four miles to the very gates of the city. Thirty-two thousand men have been defeated by 8000. The total Mexican loss is 4000 killed and wounded, 3000 prisoners, including eight generals; the American loss is 1052, of whom seventy-six are officers.
August 21 President and General Santa Anna proposes an armistice.
September 7 the armistice is broken and General Scott resumes his advance upon the city.
September 8 the General Worth division, reinforced to 3000 men, in a bloody battle captures the outpost Molino del Rey or King’s Mill, and the Casa-Mata supporting it—the two being defended by 14,000 Mexicans. American loss, killed, wounded and missing is 789, including fifty-eight officers. The Mexican loss is in the thousands.
September 12, by a feint the Scott army of 7000 able-bodied men is concentrated before the Castle of Chapultepec, situated upon a high hill fortified from base to summit and crowned by the Military College of Mexico, with its garrison of cadets and experienced officers.