Antonio might be assailed in rear.

Overlooking the road, however, as well as the issues from the
Pedregal, was a high ridge, backed by the mountains, and held by 6000
Mexicans. Opposite this ridge the Americans came out on cultivated
ground, but all further progress was completely checked. Shortly
after midday the leading brigade, with Magruder's battery on hand,
reached the summit of a hill within a thousand yards of the enemy's
breastworks. Magruder came at once into action, and the infantry
attempted to push forward. But the Mexican artillery was far
superior, both in number of pieces and weight of metal, and the
ground was eminently unfavourable for attack. Two-and-twenty heavy
cannon swept the front; the right of the position was secured by a
deep ravine; masses of infantry were observed in rear of the
intrenchments, and several regiments of lancers were in close
support. For three hours the battle raged fiercely. On the right the
Americans pushed forward, crossing with extreme difficulty an
outlying angle of the Pedregal, covered with dense scrub, and
occupied the village of Contreras. But elsewhere they made no
impression. They were without cavalry, and Magruder's guns were far
too few and feeble to keep down the fire of the hostile batteries.
"The infantry," says Scott, "could not advance in column without
being mowed down by grape and canister, nor advance in line without
being ridden down by the enemy's numerous horsemen." Nor were the
Mexicans content on this occasion to remain passively in their works.
Both infantry and cavalry attempted to drive the assailants back upon
the Pedregal; and, although these counterstrokes were successfully
repulsed, when darkness fell the situation of the troops was by no
means favourable. Heavy columns of Mexicans were approaching from the
city; the remainder of the American army was opposite San Antonio,