Alcatraz is a forbidding-looking rocky island that squats in San Francisco Bay, just a 20-minute ferry ride from Fisherman’s Wharf. It was the prison where the toughest gangsters and killers, including Al Capone and other infamous criminals served their hard time sentences.

Scarface Al and the other guys called it The Rock. Some of the more interesting historical facts about the prison island are well worth learning. 1. Alcatraz was built as an Army fort in 1854, and was first used as a prison a decade later during the Civil War. The 1849 California Gold Rush brought thousands of people to San Francisco, many of them from the Southern states. During the war, several hundred who had expressed sympathy or were openly helping the Confederacy, were arrested and sent to Alcatraz. They were held there until the end of the war.

2. The same year California’s first lighthouse was built on a high spot of the island. It was originally used as a military watchtower, and also a rotating beacon to warn ships in San Francisco harbor about rocks and other hazards.

3. There have been many movies about Alcatraz since silent film days. Two more recent starred Clint Eastwood. The 1962 movie, based on a true incident, “Escape from Alcatraz” ends without indicating whether the escape was successful or not by the prisoner portrayed by Eastwood. In a later movie, as tough guy San Francisco detective Dirty Harry, Clint used a rocket launcher to blow up the watchtower and the bad guy in it.

4. In May, 1946, five inmates murdered two guards in an escape attempt. Marine combat units were sent in, and killed three of the murderers. The other two, who had been in prison for prior murders, were later executed.

5. The Alcatraz prison was closed in 1963, and empty until a group of  75 Native Americans took it over as a protest in 1969. The occupiers claimed ownership under a 19th Century treaty with the U.S. government. There was no violence, but some buildings were damaged, and the men eventually ousted two years later by Federal marshals.

These are just a few of the many fascinating facts about Alcatraz. The Rock today is operated by the National Park Service. If you’re in San Francisco and want to explore the site, and possibly find some more secrets, check with San Francisco tour operators or go to  www.nps.gov/alcatraz