For much of the 19th century (1813-91) the keep was the focus of prison activity whilst the castle served as the Island's main gaol. Major alterations included the insertion of a stairwell within the SW corner and various breaches through the walls to reach new accommodation blocks and exercise yards constructed within the inner bailey. Some of these changes were restored once the castle ceased to be a prison, during a restoration programme conducted under Lt Governor Lord Raglan between 1904-10.