lse, and that, should he
find at the commencement of his movements one of the points of attack
abandoned, as this, for instance, he will pass by this route with all
his forces, and thus be enabled to assail our flank and turn our rear;
or, if he prefer it, he may pass on without obstruction to the City of
Mexico."

General Valencia, however, ordered a thorough reconnoissance by
General Mendoza, an engineer officer, who reported "that Padierna was
absolutely indefensible, and that it was believed best to retire for
reasons expressed in his note." General Valencia ordered Colonel
Barreiro to Zacatepetl to watch and report the movements of the enemy.
He further ordered Colonel Mendoza to occupy with his regiment the
edge of the _pedregal_, having in his front a detachment of infantry
under Captain Solos, and beyond him a detachment of cavalry. To the
left of Padierna was posted the corps of San Luis Potosi, to the right
the brigade of Lieutenant-Colonel Cabrera, and on the ridge were the
batteries and brigade of General Mejia. The supporting line were three
battalions. The reserve at Anzaldo, a mixed company of infantry and
cavalry, was the command of General Solos, supported on the right by
two regiments of infantry.

Pillow's and Twiggs's divisions were observed by Colonel Barreiro to
be moving over the mountain of Zacatepetl and the _pedregal_. On an
open ridge commanding the _pedregal_ General Valencia had planted
guns which commanded the _pedregal_ in the direction of San Augustin.
On the morning of August 19th General Santa Anna ordered two
battalions to move from Churubusco to San Antonio, Pillow's division
of the American army having moved out from San Augustin on the road to
Padierna, which was to be covered by Twiggs's division. Twiggs moved,
following Quitman, and passed beyond San Augustin. General Alvarez
closed on his rear. A working party of five hundred men under engineer
officers was detailed from Pillow's division to make the road to
Padierna practicable for artillery. While work was progressing on this
road General Scott notified General Pillow that Valencia was placing
heavy guns in position, and ordered that the work be pushed forward as
rapidly as possible. Before the road was finished half the distance
Twiggs's division passed Pillow's command, and its advance was fired
upon by the Mexicans. General Persifor F. Smith ordered the mounted
rifle regiment under Major William Wing Loring, aided by a sec