With the outbreak of hostilities at Rancho de Carricitos, both U.S. and Mexican armies accepted war had begun. Neither side waited for a formal declaration of war. General Mariano Arista began shuttling troops across the Rio Grande to besiege the isolated Fort Texas.
General Zachary Taylor expected just such a move. On May 1, 1846, Taylor marched most of his troops to his supply depot at Point Isabel on the Gulf of Mexico. It was there the veteran U.S. general would meet an incoming naval fleet carrying supplies needed to endure an extended siege. General Taylor left Major Jacob Brown, the U.S. Seventh Infantry, and portions of the Third Artillery—some 550 men—to hold the post on the river.
General Arista was not able to prevent Taylor's departure for the coast. Instead he moved quickly to surround the U.S. outpost on the river. On May 3, 1846, Mexican artillery opened fire on Fort Texas from all directions in hopes of forcing a quick surrender of its defenders.