Alcatraz Island, located in San Francisco Bay, is best known as the site of the notorious former federal prison, but its history extends far beyond that. Here are six common questions about the national landmark.

Named “Isla de los Alcatraces” by Spanish explorer Lieutenant Juan Manuel de Ayala in 1775, the 22-acre Alcatraz Island was originally a natural habitat for seabirds. In 1850, President Millard Fillmore designated it a U.S. military reservation to protect San Francisco Bay during the Gold Rush, according to the National Park Service. By 1853, construction of Fortress Alcatraz began as part of a “Triangle of Defense” (along with operations at Fort Point and Lime Point) to guard the bay.

In 1861, Alcatraz became a military prison, housing a diverse group of inmates, including military deserters and civilians accused of treason during the Civil War. Later, it held Native American prisoners, notably 19 Hopi men in 1894, who resisted federal policies to assimilate their children in distant boarding schools. The prisoner population surged during the Spanish-American War, growing from 25 inmates in 1899 to 441 by 1900.

Alcatraz was then transformed into a minimum-security disciplinary barracks emphasizing rehabilitation, but rising operational costs and the economic pressures of the Great Depression led the army to relinquish the facility in 1933.

According to the Federal Bureau of Prisons, the U.S. Department of Justice repurposed Alcatraz as a “maximum-security, minimum-privilege penitentiary” to address “rampant crime” during the 1920s and 1930s. The bureau adds that most prisoners were those “who refused to conform to the rules and regulations at other Federal institutions, who were considered violent and dangerous, or who were considered escape risks.”

The prison held several famous prisoners, including gangsters Al Capone, George “Machine Gun” Kelly and James “Whitey” Bulger, and murderers like Robert Stroud (the “Birdman of Alcatraz”).

Nicknamed “The Rock,” Alcatraz was deemed inescapable, yet the FBI reported 14 escape attempts involving 36 men during its operation. All but three were caught or died trying. The three men who were never found used plaster heads to evade bed checks and crude tools to dig holes from their cells, creating a makeshift workshop to build a raft and paddles. The FBI officially closed the case in 1979, the same year Clint Eastwood starred in the movie Escape from Alcatraz, recounting the events.

The prison closed on March 21, 1963 due to high operational costs, particularly because supplies had to be transported by boat, making it nearly three times more expensive to operate than other federal prisons. "For example, the island had no source of fresh water, so nearly 1 million gallons of water had to be barged to the island each week," states the Federal Bureau of Prisons.

In 1969, a group of Native Americans and supporters staged an occupation of Alcatraz Island, declaring it Indian land and using the protest to highlight Native American rights and issues. According to the National Park Service, it is still the longest occupation held by Native Americans in a federal facility. The demonstration lasted 19 months before federal agents removed the remaining occupiers in 1971.

In 1972, Alcatraz became part of the Golden Gate National Recreation Area and opened to the public in 1973. It was designated a National Historic Landmark in 1986. According to the U.S. General Services Administration, the island sees more than 1.4 million visitors annually, making it one of the National Park Service’s top tourist sites.