The old Melbourne Gaol was based on the design of the Pentonville Prison in London, which became the standard for mid-19th Century prisons throughout the then British Empire. Parramatta, Goulburn and Port Arthur prisons also followed the model to some extent. The Pentonville system dictated the imposition of long periods of isolation (hence the single cells), silence and constant surveillance.

This was intended to break the spirit of the prisoners so that they could be reformed. In practice, however, it more commonly drove already unstable prisoners around the twist rather than reforming them and was largely abandoned by the start of the century. Mind you, given some of the characters that were housed in this place I think having your own cell, Spartan and small as it may be as we can see from this shot and others in the gallery, may be quite a desirable situation in some ways.

Note the windows; these were constructed of two sheets of 1 inch (2.54cm) thick translucent glass set into the masonry during construction. (Not sure what they did about breakages, because not even 1" thick glass lasts forever.) They were spaced to allow a flow of air between the panes but to obscure the view. Further security was provided by external bars.