Saint Helena is a remote volcanic tropical island in the South Atlantic Ocean, belonging to the United Kingdom. The island lies some 1,950 kilometres (1,210 mi) west of the coast of southwestern Africa, and 4,000 kilometres (2,500 mi) east of Rio de Janeiro on the South American coast. It is one of three British Overseas Territory grouped as Saint Helena, Ascension and Tristan da Cunha. Saint Helena measures about 16 by 8 kilometres and has a population of 4,534. It was named after Saint Helena of Constantinople. It is one of the most isolated islands in the world and was uninhabited when discovered by the Portuguese in 1502. It was an important stopover for ships sailing to Europe from Asia and Southern Africa for centuries.