Fort Dennison is a defensive facility occupying a small island located north of the Royal Botanical Gardens in Sydney Harbour. Originally named Pinchgut, 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.