During the Mexican war he was twice severely wounded in a reconnaissance at Cerro Gordo, 1847, was engaged in the siege of Vera Cruz, the battles of Contreras, Churubusco, and Molino del Rey, the storming of Chapultepec, and the assault on the city of Mexico, and received three brevets for gallant and meritorious service.
At the base of the monument are muskets used by United States soldiers in that war and guns captured at Cerro Gordo.
He received the brevets of major for Cerro Gordo, lieut.- colonel for Contreras-Churubusco and colonel for Chapultepec. After the war he was employed in engineer work at Washington and Baltimore, during which time, as before the war, he resided on the great Arlington estate, near Washington, which had come to him through his wife.
Wool in Chihuahua, and under General Winfield Scott in the southern campaign; he was breveted major-general for gallantry at Cerro Gordo, where he was severely wounded, and he was again wounded at Chapultepec. In1849-1855he was a United States senator from Illinois; and in1858-1859was a senator from Minnesota.