The next morning, August 19, therefore--while Quitman unwillingly remained at San Agustín to guard the base,[26.7] and Worth, with his engineers and troops, continued to reconnoitre and threaten on the San Antonio side--Scott ordered a force of engineers to build a road in the other direction. Pillow's division was to furnish working-parties, and Twiggs's to clear away whatever Mexican detachments might undertake to hinder the operations; and the implied instructions were to gain and hold the San Angel turnpike, so that San Antonio could be turned. Scott did not expect or desire a general engagement at this time; but he directed Pillow to take command and employ both divisions, if a battle should be opened, promising that in such an event he would soon appear on the field. Under these instructions the troops advanced cautiously but rapidly the first mile and a quarter, constructed a road to the summit of the ridge, pulled up the guns with drag-ropes, and looked over. As the returning tide makes a sea in the Bay of Fundy, where only bare ground had been visible a few hours earlier, Valencia's army had taken possession. It was now one o'clock, and evidently road-building was over for a while.[26.11] Pillow, however, knew all about winning victories. From a central hill, Zacatepec, where he stood, he could measure Valencia's forces to a nicety, and he decided to brush them away. By his order the Mounted Rifles, particularly the advanced companies of Roberts and Porter, deployed quickly, drove the Mexican skirmishers in a handsome style from rocks and fissures, and finally occupied Padierna. At the same time and under his instructions Magruder--tall, blonde and intrepid--advanced his field battery nearly a mile without cover over that almost impassable ground, which the enemy had now barred with stone walls, planted it under the slight protection of a transverse ledge, and not long after two o'clock opened a duel with Mexican siege guns, 68-pound howitzers and many lighter pieces, more than twenty in all, at a range of about 900 yards, while brave Callender fought the howitzer battery beside him, dashing little Reno set off rockets, and Smith's and Pierce's brigades, which were presently to attack Valencia's camp, furnished support. And Pillow knew also how to "bag" a defeated enemy. So he ordered Riley's brigade to the extreme right to coöperate with the frontal attack by checking reinforcements and cutting off Valencia's retreat. Then he countermanded this order, but not in season.[26.11]