Presidio San Agustín del Tucsón was a presidio (colonial Spanish fort) located within Tucson, Arizona, United States. The original fortress was built by Spanish soldiers during the 18th century and was the founding structure of what became the city of Tucson. After the American arrival in 1846, the original walls were dismantled, with the last section torn down in 1918. A reconstruction of the northeast corner of the fort was completed in 2007 following an archaeological excavation that located the fort's northeast tower.