This fortified ranch house, or fortaleza, is the oldest documented structure to survive from the Spanish colonial period in the lower Rio Grande region. The one-room, rectangular, windowless, sandstone fortress was built to shelter ranch settlers during Indian raids. More primitive and much smaller in appearance than the nearby Jesús Treviño Fort (
SM1) in San Ygnacio, the fortaleza exhibits numerous troneras (gunports) along its exterior walls, including its parapet. Its original hand-hewn wooden beams and fireproof roof of chipichil were accurately replicated in a rehabilitation of 2006 by building conservator Frank Briscoe Jr.

Approximately 150 feet away, on the same property, a larger two-room fortified structure (1870) still stands. It has a projecting perimeter base forming a pollo, or water table, a typical building component of the region to ensure structural stability. Its lack of gunports indicates the minimized threat of Indian raids by the late nineteenth century.