Established in 1756 near the lower Trinity River in present-day Chambers County, Presidio San Agustin de Ahumada functioned as a small Spanish military garrison of roughly one officer and thirty soldiers, built to assert Spanish territorial claims along the Gulf Coast and counter French trade and settlement encroaching from Louisiana, including the expulsion of French traders in 1759. Everyday life at the post centered on routine garrison duty, patrols, and logistics, made difficult by chronic supply shortages, disease, biting insects, and the isolation of its coastal marsh setting. The presidio operated alongside the adjoining Mission Nuestra Senora de la Luz, together forming the outpost known as El Orcoquisac, meant to also missionize local Orcoquiza and other coastal native bands; missionary activity briefly expanded under Captain Rafael Martinez Pacheco, though his harsh treatment of soldiers provoked desertions, and an armed Orcoquiza uprising in 1759 further destabilized the post. With France's cession of Louisiana to Spain in 1763, the presidio's original strategic purpose evaporated, and a severe hurricane in 1766 damaged its buildings; inspector the Marques de Rubi judged the post useless in 1767, and Spanish troops formally withdrew by 1771-72, ending its sixteen years of active use. Almost no structural remains survive above ground today. Twentieth-century archaeological excavations helped confirm the site's location near Lake Miller on the Trinity's east bank, and a state historical marker, erected in 1936, now commemorates the site, which functions today as a designated archaeological district and point of historical interest rather than a developed public attraction.