Eastern State Penitentiary in Philadelphia is a former American prison operational from 1829 until 1971. It is considered to be the world’s first true penitentiary, with its revolutionary system of incarceration, dubbed the “Pennsylvania system” or separate system. The system encouraged separate confinement (the warden was legally required to visit every inmate every day, and the overseers were mandated to see each inmate three times a day) as a form of rehabilitation. Notorious criminals such as bank robber Willie Sutton and Al Capone were held inside its innovative wagon wheel design. At its completion, the building was the largest and most expensive public structure ever erected, and quickly became a model for more than 300 prisons worldwide. The prison is currently a U.S. National Historic Landmark and open to the public for tours and photography.