For around 40,000 years before European settlement commenced in the late 18th century, the Australian mainland and Tasmania were inhabited by around 250 individual nations of indigenous Australians. The written history of Australia began when Dutch explorers first sighted the landmass in the 17th century. After sporadic visits by fishermen from the immediate north, and European discovery by Dutch explorers in 1606, the eastern half of Australia was claimed by the British in 1770 and initially settled through penal transportation to the colony of New South Wales, founded on 26 January 1788. The population grew steadily in the following years; the continent was explored, and during the 19th century another five largely self-governing Crown Colonies were established. On 1 January 1901, the six colonies became a federation, and the Commonwealth of Australia was formed.