Sumatra is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the sixth-largest island in the world at 473,481 km2 (182,812 mi.2), not including adjacent islands such as the Simeulue, Nias, Mentawai, Enggano, Riau Islands, Bangka Belitung and Krakatoa archipelago.