DID a Portuguese seafarer called Christopher de Mendonca lead a fleet of four ships into Botany Bay in 1522 - almost 250 years before Captain James Cook?
The startling claim is made in a book - published today - by the retired Canberra-based science journalist Peter Trickett. Trickett believes Mendonca left irrefutable evidence of his historic voyage: a detailed and uncannily accurate map of Australia's entire east coast.
Trickett's quest began eight years ago in a Canberra bookshop where he bought a beautiful portfolio of rarely seen maps - exquisite reproductions from the Vallard Atlas, a 16th-century document so precious and delicate it never leaves its air-conditioned vault in the Huntington Library in Los Angeles.
The original Vallard Atlas contains 15 hand-drawn maps, completed no later than 1545 in Dieppe, France, and represents the entire world as it was then known to Europeans. Scholars had long asked why part of one of the Vallard maps - featuring 120 place names in Portuguese, not French - closely resembled the coast of Queensland. But they had dismissed it as a coincidence, because the map suddenly jutted out at right angles for 1500 kilometres, bearing no relation to any known coastline.
However, Trickett came up with an intriguing theory: what if the atlas compilers in Dieppe had wrongly aligned two Portuguese charts they were copying from?
He called in a computer expert who was able to cut the map in two and rotate the bottom half 90 degrees.
"Up to that point it was just a theory," Trickett says.
"But once it was rotated … the entire east coast of Australia, and part of the south coast as far as Kangaroo Island, was revealed in incredible detail."
Trickett believes the charts were made by Mendonca, who set off from the Portuguese base at Malacca with a fleet of four ships on a secret mission ordered by King Manuel I. If Trickett is right, Mendonca sailed past Fraser Island, into Botany Bay, around Wilsons Promontory and as far as Kangaroo Island before returning to Malacca via the North Island of New Zealand.
But because the Portuguese wanted to prevent other European powers learning about their discovery, Mendonca's charts were kept secret. Instead, says Trickett, Mendonca was rewarded by being made commander of the lucrative fortress at Hormuz in the Persian Gulf, where he eventually died. "His voyage ranks with that of Columbus or Magellan," says Trickett.
"But it was secret, unfortunately."
On the southern coast, Trickett says, Mendonca clearly marked many of the outstanding features: Cap Frimosa (Wilsons Promontory), Illa Grossa (Kangaroo Island), Rio Real (Spencer Gulf) and Golfo Grande (the Great Australian Bight). But the most significant feature on the Vallard map is Baia Neve. Trickett insists this is what Cook later called Botany Bay, the birthplace of modern Australia.
Beyond Capricorn: How Portuguese adventurers secretly discovered and mapped Australia and New Zealand 250 years before Captain Cook by Peter Trickett, East Street Publications, $35.