American General Zachary Taylor retreated from Fort Texas on May 1, 1846; Mexican General Mariano Arista began preparing artillery and troops from across the Rio Grande. On May 3, Arista and the Mexican Army began the Siege of Fort Texas, during the first active campaign in the Mexican–American War. This was counteracted by the United States 7th Infantry Regiment. Despite heavy strikes, Mexican General Pedro de Ampudia outlined a traditional siege to move forward. General Zachary Taylor was notified of the incident and began moving towards Fort Texas. Mexican troops intercepted them near Palo Alto, about north of present-day Brownsville, however, resulting in the first battle of the war.