As the Spanish moved North from Mexico in the 17th and 18th Centuries, they secured their territory not with forts but with missions, and these are dotted all over what is now the Southwest of the US, in varying states of preservation. There are three in what is now San Antonio, and San Jose is the largest.
It was a self-contained walled compound, containing accommodation for indians who worked the fields surrounding the compound and maintained trade with surrounding districts and missions, and for the priests who managed the mission and looked after the conversion of indians to christianity. The worker accommodation is built into the surrounding walls, and the priests had a cloistered area adjacent to the church, which is now in ruins, only the arched windowframes standing. The church still does regular parish work.
Though the architectural style of the compound and church is austere, there is an ornate window built into a side chapel of the church which looks incongruous.