Perched on a cold, foggy rock in the middle of San Francisco Bay, Alcatraz wasn't designed just to hold criminals, it was designed to break their will.

Known as "The Rock," it housed the "worst of the worst," including Al Capone and "Machine Gun" Kelly.

Alcatraz wasn't just about bars and walls. Its power was in its location and design:

• The prison was so close to the city that on quiet nights, inmates could hear the sounds of parties, music, and laughter drifting over the water from San Francisco. It was a constant reminder of the life they lost.

• The cell blocks were designed so that guards could see down every corridor from a single vantage point. Inmates never knew exactly when they were being watched, creating a feeling of constant surveillance.

• The freezing, turbulent currents of the Bay were considered the ultimate "outer wall." Officials claimed no one could survive the swim to shore.

Despite its fearsome reputation, Alcatraz was incredibly expensive to run. Every drop of fresh water had to be boated in, and the salt air eroded the buildings. It closed its doors as a federal prison in 1963.