Instead of marching on Puebla, Santa Anna turned his forces toward Queretaro, but in a few days countermarched.  After two or three maneuvers of this kind, he finally invested Puebla with about fifteen hundred cavalry and four field pieces.  He summoned Colonel Childs, who was in command, to surrender on the score of humanity.  Santa Anna represented his force at eight thousand men, and threatened assault.  Colonel Childs declined to surrender, and made preparations to resist the assault by strengthening his position.  The threatened assault was not made.  On October 1st Santa Anna raised the siege of Puebla and marched toward El Pinal to intercept a train of wagons with supplies and re-enforcements, leaving General Rea with sufficient force to continue operations against the Americans.  The Americans were so annoyed by continuous firing from the housetops that Captain William F. Small, First Pennsylvania Infantry, was ordered to dig through the walls of the houses until he had gained a point which would command a barricade that had been thrown up by the Mexicans.  The enemy was driven off, leaving seventeen dead on the ground; the barricade was then burned.  Hostile parties were constantly annoying the garrison, until two companies of the First Pennsylvania regiment were sent out and dispersed them.  Many skirmishes took place, which invariably resulted disastrously to the enemy.

General Joseph Lane’s efforts to exterminate the roving bands of guerillos and rancheros involved great rapidity of movement, and he had officers and men under his command eminently fit for such service.  One of the most pestiferous of the guerillo leaders was a Catholic priest called Padre Juarata.  He seemed to be everywhere at once, and notwithstanding his party was frequently met by the Americans, sometimes surrounded and always beaten, yet the Padre adroitly managed to get out of every trap and escape.  Being a priest, he was always ready and willing to administer the last rites of the Church to friend or foe.

While the army was at Puebla, General Scott organized a company of Mexicans under command of one Dominguez, which was regularly mustered into the service of the United States.  A battalion of deserters from the American army, known as the San Patricio Battalion, composed almost wholly of Europeans, was organized under the command of one O’Riley.  These two commands met in battle in the convent of Churubusco, and fought each other with great desperation.  The Mexicans under Dominguez entered Churubusco with the American army, and met the execration of their countrymen, who denounced them as traitors.  The American deserters (the San Patricio Battalion) were captured at Churubusco, tried by court-martial, and all but sixteen sentenced to death and executed.  Some were pardoned, and O’Riley, their leader, was branded with the letter D on his cheek and released.  This clemency was shown him because he deserted before hostilities commenced.