Saint Helena, named after St Helena of Constantinople, is an island of volcanic origin in the South Atlantic Ocean. It is part of the British overseas territory of Saint Helena, Ascension and Tristan da Cunha which also includes Ascension Island and the islands of Tristan da Cunha. The island has a history of over 500 years since it was first discovered as an uninhabited island by the Portuguese in 1502. Britain's second oldest remaining colony (after Bermuda), Saint Helena is one of the most isolated islands in the world and was for several centuries of vital strategic importance to ships sailing to Europe from Asia and South Africa. For several centuries, the British used the island as a place of exile, most notably for Napoleon Bonaparte, Dinuzulu kaCetshwayo and over 5,000 Boer prisoners.