How and when did the Mission San Antonio de Valero become a military fort?

Though Indian depredations prompted earlier fortifications to the mission compound (probably in response to such instances as the San Saba massacre) the changes that would forever associate the mission as a fortress did not occur until permanent military occupation took place at the beginning of the 19th century.

In the early 1800's, expansionists, like Aaron Burr, called for the invasion of Spanish territory causing Spain to look toward the United States with great anxiety. With the purchase of the Louisiana territory in 1803, the Spanish made plans to repel any possible foreign invasion by concentrating Spanish troops on the Texas frontier. As the first of several reinforcement efforts, the Alamo de Parras Company marched under orders from Chihuahua to Texas to San Antonio de Béjar [Béxar] to bolster the Béxar Presidio. Most of the soldiers arrived on the Rio San Antonio by January 1803 with their families following that spring.

The existing soldiers of the Béxar Presidial Company had already established their own residences in the area and so readily relinquished their quarters to the new arrivals. What the company found was less than satisfactory as Francisco Amangual, the commander of the Alamo de Parras Company, found the barracks on Plaza de Armas in poor condition. Evaluating his options, he moved his men and their families across the San Antonio River and into the partially abandoned mission of San Antonio de Valero that had been secularized in 1793. The old mission convento and rooms along the West Side of the plaza were in better condition and offered more room and protection. The courtyard was converted to a corral and the sacristy of the partially completed church became the chapel.

There were more than two hundred men, women and children in the Alamo de Parras community living together within the mission's walls. The lower floor of the derelict convent, or the Long Barracks, housed the unmarried soldiers. Soldiers with families lived in adobe shelters adjoining the exterior wall of the compound's enclosure. Others lived in crude huts called jacales. Eventually, Indian raids forced them to move inside the enclosure.

In the years that followed, the Alamo de Parras Company slowly rebuilt and reinforced the mission compound. By 1805, they founded the first military hospital in San Fernando de Béjar that was situated in the upper level of the mission's convent. It served both the military and civilian populations. In 1809, rumors of an invasion by the United States spread across the province. The Alamo de Parras Company promptly ordered materials to add 834 varas of battlement to the existing walls of the enclosure. Part of this construction included the southernmost wall with a large gate separating a barrack from a guardhouse and jail.

The Alamo de Parras company continued to occupy their "fort" until 1830, when the mission compound again was abandoned for a two year period during the company's occupation of Fort Tenoxtitlan in Southeast Texas. The failure of that endeavor returned the company to the fort in 1832 where they remained until December 10, 1835 when General Cos surrendered at the "Battle of Béxar", evacuating his Mexican garrison of 1,105 men. A Texian garrison of about 104 men took possession of the Alamo.

As the war with Mexico escalated, there were complaints that the Alamo had been stripped of cannons and supplies to reinforce efforts in Matamoros. General Sam Houston sent Jim Bowie with about 20 men to the Alamo to inspect it, assuming that he would recommend evacuation. He remained with others to defend the mission and in the March of 1836 the Alamo forever took its place in history as El Fuerte del Alamo.