The Military Origins of Alcatraz

Before it was a legendary federal prison, Alcatraz started as a military fortress in the 1850s. The site spent decades as a holding ground for soldiers before becoming the high-security penitentiary known as The Rock.

Long before the famous inmates arrived, the island served as a strategic defensive fort for the San Francisco Bay. The structure you recognize today was actually constructed between 1910 and 1912 to function specifically as a military prison. This transition from a defensive stronghold to a house for the nation's most dangerous criminals defined its rugged reputation. It remains a fascinating example of how a site can completely reinvent its purpose over a century.