Fort Denison is a defensive facility occupying a small island located north of the Royal Botanical Gardens in Sydney Harbour. Originally named Pinchgut (possibly owing to the poor quality and quantity of food given to imprisoned convicts), the island was used as a place of confinement for recalcitrant convicts during the early period of British settlement. The fortress, which features a distinctive martello tower, was built in the mid 19th century as a defence against a feared Russian invasion during the period of the Crimean War, and occupies the entire island. It is reputedly the last martello-style fortification built by the British Empire.