Designed by English philosopher Jeremy Bentham in the late eighteenth century, the design was all about observation and surveillance. It was intended to allow the prisoners to be observed without them knowing if or when they were being watched. Bentham described it as "a mode of obtaining power of mind over mind" It was intended to be cheaper than other prisons, as it required fewer staff. The design incorporates a tower central to a circular building that is divided into cells, each cell extending the entire thickness of the building to allow inner and outer windows. The occupants of the cells are thus backlit, isolated from one another by walls, and subject to scrutiny both collectively and individually by an observer in the tower who remains unseen. The prisoners would also be used as menial labour walking on wheels to spin looms or run a water wheel. This would decrease the cost of the prison and give a possible source of income. Bentham devoted a large part of his life and fortune to promote the construction of a prison based on his scheme. But was not successful in his lifetime in achieving this. The 19th century convict gaol Millbank was built to this design as was Port Arthur, in Tasmania, Australia. Many modern prisons built today are built in a "podular" design influenced by the Panopticon design, in intent and basic organisation if not in exact form.