The Chapel is the oldest section of the Presidio La Bahía and was built to give the soldiers stationed at the fort a place to worship.

Mass is still held every Sunday at 5:00 p.m. just as it has been almost continuously since the Presidio was relocated here in 1749. One of the oldest churches in America, it is also one of the only buildings in existence that has its original "groin vaulted ceiling" in place.

The first Texas Declaration of Independence from Mexico was signed on this altar on December 20, 1835 and Fannins men were imprisoned here before their execution.

The beautiful fresco behind the altar was done in 1946 by Antonio Garcia who was known as the "Michelangelo of South Texas".