The Eastern State Penitentiary is a former prison in Philadelphia. The penitentiary refined the revolutionary system of separate incarceration (known as the Pennsylvania system), which emphasized principles of reform rather than punishment. When the Eastern State Penitentiary was erected in 1829, it was the largest and most expensive public structure in the country. The prison was closed and abandoned in 1971, as it became too expensive to maintain. It now is open as a museum, but is minimally maintained, making it an exciting place for a photographer.