The Portuguese Questions
While there's no direct evidence to support the notion that the Portuguese sailed down Australia's east coast in the early sixteenth century, it seems safe to assume they knew the continent was there, even if they didn't reach it.
Portuguese voyages may have been the source for the coastline labelled Jave la Grande on maps drawn in Dieppe in the first half of the 15th century.
Kenneth Gordon McIntyre's The Secret Discovery of Australia suggests all those maps were copies of a Portuguese chart, stolen, subsequently lost, and more than likely the work of Cristóvão de Mendonça, with 1521–1524 as the most likely time frame.
McIntyre suggests there were official records of such a voyage, but the 1755 Lisbon earthquake destroyed the documents.
Other writers offer variations on the same theme. While most of it is hypothetical, any discussion of northern Australia's "discovery" must consider the Portuguese questions.
