Alcatraz Island is a small island 1.25 miles offshore from San Francisco, California, United States. The island was developed in the mid-19th century with facilities for a lighthouse, a military fortification, and a military prison. In 1934, the island was converted into a federal prison, Alcatraz Federal Penitentiary. The strong currents around the island and cold water temperatures made escape nearly impossible, and the prison became one of the most notorious in American history.