General Valencia had not yet faced U.S. troops in battle, and did not consider the spot that Santa Anna had ordered him to at San Ángel to be a defensible position. He disobeyed orders and moved his infantry and cannons to just south of Padierna. Valencia had not expected the U.S. forces to be able to cross the lava field at El Pedregal, considering it impassable terrain and a natural defense. Intending to flank San Antonio, Scott ordered Capt. Robert E. Lee to build a road across El Pedregal so he could enfilade San Antonio to the north of San Agustin. On the morning of 19 August, Lee's men met Mexican pickets, which Major William W. Loring's companies cleared at Padierna, only to come under fire from Valencia's 22 pieces of artillery west of El Pedregal and north of Contreras. When told of the American movement across El Pedregal, Valencia exclaimed, "No! No! You're dreaming, man." The U.S. forces took heavy casualties and Valencia thought at this point he was winning the encounter.