TOP: There are thick walls with round watch towers at each corner. Mounted guards patrolled outside those walls.
So it was for security that the Coahuitecans gave up their culture and became ancestors of some of today’s Hispanic Americans. There is no modern group called Coahuitecans.

BOTTOM: inside - The San Antonio missions were not manned with a significant number of soldiers, so the people living inside had to learn basic defensive skills. To help matters, the mission walls, which served the same purpose as the walls of a typical fort, were often built to include bastions: common defensive structures of a fort that protrude out from the walls at the corners. Bastions allow armed men and cannon located inside to shoot parallel along the wall at enemies who cannot be shot at by those stationed directly on the wall itself. Only one bastion remains at Mission San José, and this was also reconstructed by the WPA.