The first Australians are believed to have arrived by boat some 50-60,000 years ago with the northern coastline of the continent a likely beach-head. The prospect of intact or even partial remains of ancient watercraft turning up in the archaeological record is remote. The expansion and contraction or the coastline over the last 60,000 years means that early landing sites would have been inundated as sea levels rose and fell, and the organic materials, perhaps wood or other plant material, from which such early watercraft would have been constructed have long since rotted away. Rock art assemblages from Australia's north then, represent the most likely record of venturesome mariners, who may have reached the coast over the millennia since initial occupation, or of watercraft constructed by Aboriginal inhabitants settled in coastal regions.