Answer: Santa Anna must have known the Alamo would be no match for his forces. Built by Spanish priests with Indian labor, the mission was never meant to be a fortress. Lacking extended walls or rifle parapets, it was almost impossible to defend—not because it was too small but because it was too big.
Fostered by a desire for vengeance, on April 21, 1836, at the close of the rebellion, the Texans defeated the Mexican Army. Texans had pushed all Mexican forces out of Mexico's Texas several months ago. There were then about 100 Texans guarded in the Alamo.