Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. It is the largest country by area in Oceania and the world's sixth-largest country. Australia's population of nearly 26 million, in an area of 7,617,930 square kilometres, is highly urbanised and heavily concentrated on the eastern seaboard. Canberra is the nation's capital, while the largest city is Sydney, and other major metropolitan areas include Melbourne, Brisbane, Perth, and Adelaide. Various waves of Indigenous Australians inhabited the continent beginning about 65,000 years ago, prior to the first arrival of Dutch explorers in the early 17th century, who named it New Holland. In 1770, Australia's eastern half was claimed by Great Britain and initially settled through penal transportation to the colony of New South Wales from 26 January 1788, a date which became Australia's national day.