General Mariano Arista believed that Resaca de la Palma, a ravine hidden by thickets, offered the strongest available position for his army. This former bed of the Rio Grande served as a natural defense for Mexican infantrymen lined up along both sides of the resaca, while thick undergrowth would protect them from the U.S. artillery that had been so deadly the day before at Palo Alto. As Zachary Taylor approached on the morning of May 9, Mexican officers believed they were ready to halt his advance toward Fort Texas, and Romulo Diaz de la Vega later recalled such confidence that he said he would have wagered $100,000 in silver that no 10,000 men could have driven them from their positions.