In 1846, United States troops marched south from Point Isabel to relieve the siege of Fort Texas, and battles broke out on the prairie of Palo Alto on Friday, May 8th, and at Resaca de la Palma on Saturday, May 9th. Two weeks before the main armies clashed here, Mexican cavalrymen first skirmished with U.S. troops in Rancho de Carricitos, a settlement 25 miles to the west, an incident that led to a declaration of war by the U.S. Congress. General Taylor had ordered an earthen fortification built on the north bank of the Rio Grande near today's downtown Brownsville, and General Arista besieged Fort Texas for six days, sparking battles at Palo Alto and Resaca de la Palma. In the first clash of the war at Palo Alto, U.S. cannonfire devastated the Mexican forces, leading General Mariano Arista to withdraw his army to Resaca de la Palma. The resaca bed still follows the same wandering course, traces of dense chapparal remain, and the modern highway crosses the ravine at the same point that the road crossed during the war.