Tucson is likely one of the oldest continually inhabited cities in the country, with archaeological evidence of human life dating back to 12,000 B.C. Later, the Hohokam natives inhabited the area from 200 A.D. through the 1500s. The Spanish arrived in 1539 and missionaries came up from Mexico in the 1600s to convert the O’odam natives to Christianity. In the late 1600s, the Jesuit Father Eusbio Kino founded the missions of Guevavi, Tumacacori, and San Xavier del Bac, as well as a number of visitas including one at Tubac.
On August 20, 1775, Irishman Hugo O’Conor established the Presidio de San Augustin Del Tucson—the site of present day Tucson—along the banks of the Santa Cruz River. In 1821, the Mexican-Spanish War was finally won after a decade of fighting. Mexico became independent from Spain and took Tucson as its northernmost outpost. Tucson became a boom town as people traveling to the California Gold Rush passed through on the now well-traveled road. When the Civil War began, Arizona seceded from the Union and became part of the Confederacy. However, it was recaptured by the Union in 1862, and became a separate territory.
When the railroad arrived in 1880, Tucson was the largest settlement between San Antonio and the West Coast, and the town quickly benefited from the availability of Eastern building materials. The railroad also brought wealthy Americans seeking to invest in mining, ranching, retailing and agriculture. Electric lighting arrived in 1883, and in 1885, the territorial legislature authorized the state university for Tucson. Before it became the University of Arizona, it was the Arizona Territorial University, opening in 1891. The first class of 32 students met in the Old Main building, which is still in use today.