The hill was formerly the site of a fort which was later used as a prison. The Old Fort Prison complex is known as Number Four. The original prison was built to house white male prisoners in 1892. The Old Fort was built around this prison by Paul Kruger from 1896 to 1899 to protect the South African Republic from the threat of British invasion. Later, Boer military leaders of the Anglo-Boer War were imprisoned here by the British.