City (pop., 2000: 486,699), southeastern Arizona, U.S. It lies along the Santa Cruz River on a Sonoran Desert plateau rimmed by mountains.
In 1700 the Spanish founded a mission nearby, and in 1776 the small walled pueblo of Tucson was made a Spanish presidio (fort). It remained the province's military headquarters under Mexican rule. The U.S. acquired the territory through the 1853 Gadsden Purchase . It was the territorial capital from 1867 to 1877. It grew with the arrival of the railroad in 1880 and the discovery of silver at nearby Tombstone and copper at Bisbee. Its dry, sunny climate and unique desert locale have made it a popular tourist and health resort and retirement community. It is the seat of the University of Arizona (1885).