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 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.

Tucson flourished under Spanish rule, but the population didn't exceed 500 until much later, when the United States controlled the city.

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, Papago and primarily the Apache.

Over Tucson's history, several different Native American groups lived in the city and the down river at the villages of Tubac, Tumacacori and elsewhere.

Groups of Pimas, Apaches, Papago, Oaptas, Seris, and others, all eventually lived at the Spanish settlements in the Santa Cruz River Valley.

Tumacacori had about 100 Spaniards during its peak years, and the remaining population of the forts and villages were Native American who usually outnumbered the Spanish by dozens to hundreds.

The wars grew into sort of a stalemate; eventually the Spanish growth in the presidio topped off resulting in the small company size garrisons.

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.

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.

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.

Apaches remained a serious threat and most of the Spanish frontier settlements in Arizona and New Mexico were abandoned and the populations fled south.

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.

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 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.

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.

After a raiding campaign into American territory against frontier settlements and the Bascom Affair in which Cochise's brother was killed, Chiricahua Apache bands began to form alliances with each other.

Apaches were at their high point and controlled almost everywhere around the region but influence was weaker northwest of Tucson in what is now the Tohono O'odham reservation.

When the American Civil War began, all of the forts protecting Tucson were abandoned and the Butterfield Overland Mail company closed just after.

Beginning just after the 1856 establishment of American Tucson, settlers in the southern New Mexico Territory began petitioning the government for separation.

A company of Confederates under Captain Sherod Hunter reinforced the militia of Tucson in late April 1862 and held a flag raising ceremony on May 1.

The company was composed primarily of militia from Doña Ana, the Arizona Rangers, of which men from Tubac had joined after escaping their town a year earlier.

Hunter dispatched several parties on foraging missions, they skirmished with Apaches twice in the Dragoon Mountains, and he sent a request to his superiors for more reinforcements.

A rebel squad under First Lieutenant Jack Swilling burned Union supplies at Stanwix Station on March 30, 1862, and skirmished with the Californians.

Rebels later fought the Battle of Picacho Pass just north of Tucson as the Union army approached the presidio.

After the Civil War, the fortress would no longer play a direct role in warfare, though the presidio walls would continue to serve as sought-out refuge by settlers until Geronimo's surrender in 1886.

By the Mexican Revolution of 1910, the next war fought in southern Arizona, only one portion of the remaining four presidio walls still stood, the others were apparently buried or demolished for new development around the turn of the 20th century.