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, five miles distant, on the far side of the Pedregal, and no support could be expected.  To add to their discomfort, it rained heavily; the thunder crashed in the mountains, and torrents of water choked the streams.  The men stood in the darkness drenched and dispirited, and an attack made by a Mexican battalion induced General Pillow to withdraw Magruder’s battery from the ridge.  The senior subaltern had been killed. 15 gunners and as many horses had fallen.  The slopes were covered with huge boulders, and it was only by dint of the most strenuous exertions that the guns were brought down in safety to the lower ground.

A council of war was then held in Contreras Church, and, contrary to the traditionary conduct of such conventions, a most desperate expedient was adopted.  The Mexican reinforcements, 12,000 strong, had halted on the main road, their advanced guard within a few hundred yards of the village.  Leaving two regiments to hold this imposing force in check, it was determined to make a night march and turn the rear of the intrenchments on the ridge.  The Commander-in-Chief was beyond the Pedregal, opposite San Antonio, and it was necessary that he should be informed of the projected movement.