The battle of Palo Alto, the first major engagement of the Mexican War, was fought north of Brownsville on May 8, 1846, between American forces under Gen. Zachary Taylor and Mexican troops commanded by Gen. Mariano Arista. Earlier, on April 23, Mexico had proclaimed a "defensive war" against the United States, which had annexed Texas. On May 12, after hostilities had begun on Texas soil, the United States declared war on Mexico. The battle, which began about 2:00 P.M. and lasted until twilight, resulted in a standoff. Darkness ended the action, and both armies bivouacked on the battlefield. That night Mexican soldiers buried their dead at Palo Alto. Of 3,461 troops that formed the Mexican Army of the North, Arista's commissary reported 102 killed, 129 wounded, and 26 missing, including deserters. Lt. George Meade, who interrogated captured Mexican officers, concluded that Mexican losses numbered 400 men. The American army, which totaled over 2,200 soldiers, reported five dead and forty-three wounded. Arista's adjutant, Jean Louis Berlandier, however, stated that American casualties were "about 200 dead and wounded."
At Palo Alto Taylor tested the superiority of the so-called "flying artillery" developed by Maj. Samuel Ringgold, who was mortally wounded in the battle. Guns were mounted on light carriages drawn by specially trained teams of horses and could be moved quickly for tactical advantage. Although soldiers on both sides clamored for the traditional bayonet charge across the field, the artillery duel dominated the action. The last maneuver at Palo Alto, nonetheless, was a desperate Mexican charge at sunset. Afterwards, the action tapered off. To neutralize the American artillery advantage at Palo Alto, the Mexican army moved southward at dawn on May 9 to Resaca de la Palma. Before it could regroup, Taylor charged and defeated Arista's army. Shortly, the Americans captured Matamoros, and Arista retreated southward toward Monterrey. Other notables at Palo Alto included Gen. Pedro de Ampudia, Gen. Anastasio Torrejón, Col. José López Uraga, Gen. William J. Worth, Lt. Ulysses S. Grant, and Texas Ranger captain Samuel H. Walker.