Franciscan missionaries chose a site west of the San Antonio River to establish Mission San Antonio de Valero. Moved twice, the mission's final location (then in the town of Bejar now known as the city of San Antonio) was established in 1724.
A church (today the best-known "face" of the Alamo) was started in 1744. Fifty years later, by order of the King of Spain, the mission was secularized. Put to various uses thereafter, it was a military post by 1803 when troops from the vicinity of El Alamo (a town in Coahuila and the likely source of the enduring name) arrived.
Those walls, and cannon located inside, were enough to give the Alamo's defenders twelve days (during late February and early March of 1836) to resist Santa Anna's siege. If the people inside could not hold out, however, Mexico's Tornel Decree insured that no quarter (scroll down 80% for its meaning) would be given to any survivors.
Two men jointly commanded the defenders: William Barrett Travis was in charge of the regular army while James Bowie headed up the volunteers. (At the time, that was a common way of running a mission in the Texas territory.)
Both sides had very different views of the impending showdown. Travis, in a now-famous letter written (and dispatched) on the second day of the siege (February 24, 1836) tried to recruit reinforcements:
To the People of Texas & all Americans in the world--
Fellow citizens & compatriots--I am besieged, by a thousand or more of the Mexicans under Santa Anna -- I have sustained a continual Bombardment & connade for 24 hours & have not lost a man -- The enemy has demanded a surrender at discretion, otherwise, the garrison are to be put to the sword, if the fort is taken -- I have answered the demand with a cannon shot, & our flag still waves proudly from the walls -- I shall never surrender or retreat. Then, I call on you in the name of Liberty, of patriotism & everything dear to the American character, to come to our aid, with all despatch -- The enemy is receiving reinforcements daily & will no doubt increase to three or four thousand in four or five days. If this call is neglected, I am determined to sustain myself as long as possible & die like a soldier who never forgets what is due to his own honor & that of his country -- Victory or Death
William Barret Travis
Lt. Col. comdt
P.S. The Lord is on our side -- When the enemy appeared in sight we had not three bushels of corn -- We have since found in deserted houses 80 or 90 bushels & got into the walls 20 or 30 head of Beeves --
Santa Anna, on the other hand, viewed Travis and the defenders as insurgents. A circular distributed by the Mexican government's Minister of Relations noted:
The colonists established in Texas have recently given the most unequivocal evidence of the extremity to which perfidy, ingratitude, and the restless spirit that animates them can go, since -- forgetting what they owe to the supreme government of the nation which so generously admitted them to its bosom, gave them fertile lands to cultivate, and allowed them all the means to live in comfort and abundance -- they have risen against that same government, taking arms against it... [while] concealing their criminal purpose of dismembering the territory of the Republic.
It would surely be a fight to the death.