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 1856, 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.
A company of Spanish Army soldiers, led by Captain Hugh O'Conor, an Irish mercenary working for Spain, selected the location of the Presidio San Agustin del Tucson on August 20, 1775. The site was on the east terrace overlooking the Santa Cruz River floodplain. Nearby was the O'odham village of Cuk Ṣon [tʃʊk ʂɔːn] at the San Agustin Mission. The name (also written S-cuk Son, Ts-iuk-shan, Tu-uk-so-on or Tuqui Son) means "black base", referring to the base of Sentinel Peak.
The following year, soldiers marched north from Tubac Presidio and began construction of the fort. Initially, it consisted of a scattering of buildings, some inside a wooden palisade. Mismanagement of the funds that were to be spent on adobe walls stalled their construction. A near disastrous attack by Apache raiders in June 1782 resulted in renewed efforts to complete the fort, which was accomplished in May 1783. The fort measured about 670 ft (200 m) to a side with square towers at the northeast and southwest corners. The main gate was on the center of the west wall, the presidial chapel was located along the east wall, the commandant's house was in the center, and the interior walls were lined with homes, stables, and warehouses. The massive adobe walls required constant maintenance, especially in times when attacks by Native Americans were anticipated, mostly from Apache. The fortress remained intact until the American arrival in 1856, two years after the Gadsden Treaty transferred southern Arizona to the United States. Afterward, it was rapidly dismantled, with the last standing portion torn down in 1918.
Tucson flourished under Spanish rule. In 1797 the population of the Presidio was 394, rising to 473 in 1831, 509 in 1848, and 575 in 1853. The colony managed to grow with the help of the fort and its occupants, who launched several expeditions into Indian country to fight the Seri's, Opatas, and primarily the Apache. The expeditions sought to prevent raids on Spanish property and civilians. O'odham, Pima, and Gileno lived nearby at the San Agustin Mission. In 1792, Apaches settled to the northeast of the fortress.
Fort Tubac was abandoned several times over 110 years due to repeated attacks at or near the fort. The garrisons remained relatively small, usually cavalry and some artillery. Lt. Juan de Olivas took command of Tucson after O'Connor from 1775 to 1777; Allande commanded the Tucson Presidio during four different attacks. He also commanded many of the advances into Apacheria and Seri country. Native warriors also contributed to the Tucson Presidio's defense several times during its history of fighting Apaches, sometimes because the natives allied with the Spanish were already long-time enemies with the Apache. The wars grew into sort of a stalemate; eventually the Spanish growth in the presidio topped off resulting in the small company size garrisons. The Spanish at any given point had fewer than 300 soldiers in all their presidios and settlements in the area. Presidio Santa Cruz de Terrenate was built along the San Pedro River southeast of Tucson in 1776, by 1780 it had already been abandoned due to Apache attacks. Presidio de San Bernardino was built just east of the present day Douglas, Arizona, in 1776 but was also abandoned in 1780. The contingents from most native groups which helped the Spanish were typically very small, about fifteen men but the Pimas contributed dozens of warriors to Captain Allande during the years who fought in most if not all of the frontier expeditions. Despite being outnumbered by the thousands, the Spanish held the majority of their settlements but could not decisively defeat the natives and stop them from raiding. Tucson became a Mexican town in 1821.
When Mexico achieved its independence from Spain in 1821, the Tucson Presidio still had a Spanish garrison that accepted Mexican freedom, likely because the Spanish aristocracy's hold on northern Sonora wasn't broken as result of the war. The aristocracy supported the independence of their country which fueled the rebellion, many also led the armies that won the war. Since 1775 and even longer due to the Pima villages, Tucson has always been inhabited, unlike several other Spanish settlements in the area. During the Mexican period at least seventy-five percent of Tucson was populated by Native Americans. After independence Mexico slipped into a depression and frontier colonization quickly became under-supplied with both men and food, old alliances between Spain and the natives ended. Other tribes continued to be peaceful, the Pimas remained friendly along with Yaquis and a few other groups in southern Arizona. Apaches remained a serious threat and most of the Spanish frontier settlements in Arizona and New Mexico were abandoned and the populations fled south. Generally the Mexicans remained only in the coastal states of Texas and California, creating more Indian country in between Mexico City and California. Landlocked settlements in what is now northern New Mexico survived with Tucson and a few other mission towns such as the San Xavier and the Tumacacori Mission. Apaches continued raiding and skirmished with Mexicans just outside the Presidio several times, they raided the livestock just like they did the Spanish herds. The Mexicans were less able to defend themselves due to the depression.
By the time the war between the United States and Mexico began in 1846, the depression was over and Mexican Army forces occupied the Tucson presidio. The area was prospering and held its largest garrison of around 200 dragoons or infantrymen with two cannons. In 1846 as the United States Army's Mormon Battalion moved through present day Arizona, they nearly fought a battle with the Mexican army as they approached the fort from the southeast. The Americans were on their way to reinforce the United States Navy's campaign against California. Mormon forces captured the presidio just after the Mexican commander Captain Antonio Comaduron decided not to fight; instead he withdrew his garrison to San Xavier and then to Tubac. The Mormons eventually left Tucson and it was reoccupied by the Mexicans. The war ended with a United States victory and the Mexican Cession in which the Mexican Government sold the Americans most of what is now the southwest United States in 1848. Tucson became part of the American New Mexico Territory after the Gadsden Purchase in 1853. Though the land was purchased the Mexican garrison did not leave the Tucson Presidio until March 1856. The majority of Mexican residents remained behind.
The United States Army took control of the Tucson Presidio in 1856 after eighty-one years in existence, and the city began to thrive once more. Famous military figures, prospectors, outlaws and warriors would all become part of Tucson's culture more than ever before. With the discovery of precious minerals in the area in the 18th century by the Spanish and in the 1860s by Americans, mining camps and later mining towns were built all across the desert frontier around Tucson. From 1850 to 1920, mining camps became the center of industrialization, before agriculture and ranching provided the best opportunity of prosperity along the Santa Cruz. The period from 1870 and on is when the speed of settling the frontier became most rapid around Tucson. Most of Arizona's towns and cities were built at this time. Hostile natives remained a problem for the development of unsettled land and continued until the late 1880s. Tubac was populated by Americans just after the Mexican War. A mining company town was made of the presidio which again made Tucson a little less isolated. During the early American period, the population grew for the first several years until a major outbreak of the Apache Wars between the Chiricahuas and the American Civil War which ended up creating Arizona into the state it is today. The Chiricahua Apache were commanded by the War Chiefs Mangas Coloradas, Cochise and Geronimo. They and their allies fought primarily a guerrilla war against the remaining Mexican and new American settlements throughout the Gadsden Purchase area, all of which was considered traditional lands of the Apache. The American Indian Wars ended in Arizona, where military campaigns against Native Americans continued as late as 1918.