The Presidio was originally a Spanish fort sited by Juan Bautista de Anza on March 28, 1776, built by a party led by José Joaquín Moraga later that year. In 1783, the Presidio's garrison numbered only 33 men. Upon Mexican independence from Spain in 1821, it was briefly operated as a Mexican fortification. The Presidio was seized by the U.S. military at the start of the Mexican–American War in 1846. It was officially re-opened by the Americans in 1848 and became home to several army headquarters and units, the last being the United States 6th Army. Several famous U.S. generals, such as William Sherman, George Henry Thomas, and John Pershing, made their homes here.