Tucson is a city on the Santa Cruz River, the seat of Pima County in southern Arizona, in the United States of America.

As of the 2000 census, Tucson is the second largest city in Arizona, after Phoenix.

Situated in a high desert valley and surrounded by mountains, the city’s dry, sunny climate has contributed to its growth as a tourist, retirement, and health center.

The city also has an expanding industrial economy based on the manufacture of optical, aerospace, and electronic equipment. Federal, state, and local governments and educational institutions are major employers. Davis-Monthan Air Force Base is in the area.

Commercial air transportation is provided through Tucson International Airport.

Tucson is the seat of the University of Arizona (1885). Other educational institutions include the University of Phoenix (Tucson) (1979) and a community college.

The Saint Augustine Cathedral (begun 1896) is a noted landmark in the city. Nearby is the Barrio Histórico, a concentration of adobe buildings from the late 1800s.

Tucson has numerous museums, prominent among them the Arizona State Museum, with one of the most comprehensive collections about the Hohokam and Mogollon peoples; the University Museum of Art, with a noted collection of sculpture; the Tucson Museum of Art; and the Arizona Historical Society Museum.

Near the city is the Arizona-Sonora Desert Museum, which combines aspects of a zoo and historical museum.

Other major attractions are Old Tucson, a movie set re-creating the city in the 1860s; Kitt Peak National Observatory, one of the world’s largest collections of optical telescopes; and Biosphere II, containing several ecosystems sealed inside an airtight glass structure.

Desert environments are preserved in Saguaro National Park and Tucson Mountain Park.

The name Tucson is derived from a Tohono O’Odham, a Papago term roughly translated as "spring at the foot of black mountain".

Native American peoples had long lived in the Santa Cruz Valley when first contacted by Europeans. Spanish Jesuit Eusebio Kino encountered a Native American settlement on the site of Tucson in 1694; he returned in 1700 to found the Mission San Xavier del Bac to the south of the village.

A fine example of Spanish mission architecture, the mission on the Tohono O’Odham Indian Reservation is one of the region’s principal attractions.

In 1776, the Spanish established a presidio, or military garrison, at Tucson, and a town eventually developed within its walls. Control of the region passed from Spain when Mexico gained independence in 1821. Tucson became a possession of the United States with the Gadsden Purchase in 1853.

In 1862, during the American Civil War, the town was held briefly by Confederate soldiers. Tucson served as the capital of the Arizona Territory from 1867 to 1877. The city was accessible by railroad by 1880.

The city’s growth accelerated after World War II (1939-1945), as many military people who had been stationed nearby returned to live. Retirees and companies have also relocated to the city.