Governor Phillip reports back to Britain on early estimates of the Aboriginal population:

The natives are far more numerous than they were supposed to be. I think they cannot be less than fifteen hundred in Botany Bay, Port Jackson, and Broken Bay, including the intermediate coast. I have traced thirty miles inland, and the having lately seen smoke on Landsdown Hills, which are fifty miles inland, I think leaves no doubt but that there are inhabitants in the interior parts of the country.

Governor Phillip to Lord Sydney, 9 July 1788. Historical Records of New South Wales, Volume 1, Part 2, p. 153.