How many troops did Santa Anna employ for his attack on the Alamo?

The Battle of the Alamo (February 23 - March 6, 1836) was a pivotal event in the Texas Revolution. Following a 13-day siege, Mexican troops under President General Antonio López de Santa Anna launched an assault on the Alamo Mission near San Antonio de Béxar (modern-day San Antonio, Texas, United States), killing all of the Texian defenders. Santa Anna's cruelty during the battle inspired many Texians-both Texas settlers and adventurers from the United States-to join the Texian Army. Buoyed by a desire for revenge, the Texians defeated the Mexican Army at the Battle of San Jacinto, on April 21, 1836, ending the revolution.

400 troop reserves were sent to Alamo to assist in the battle.