Long before Captain Cook landed at Botany Bay and later raised the flag for England, there was a widespread belief in the existence of a mysterious great southern land.
Initially that stemmed from nothing more than a theory that land in the Northern Hemisphere should be balanced by land in the Southern Hemisphere.
However, as the age of discovery unfolded from around 1500, explorers and mariners, Dutch, Spanish and Portuguese, reported seeing bits of an unknown land.
One was Spanish mariner Luis Vaz de Torres whose voyage in 1606 skirted the southern coast of New Guinea and passed through what is now known as Torres Strait.
When Britain seized Manila from Spain in 1762, Torres' account caught the eye of geographer and hydrographer Alexander Dalrymple who became lead proponent for the existence of a great undiscovered land in the southern hemisphere.
The Scot's writings featured much imagination but minimal actual knowledge - he posited a nation of 50 million inhabitants. This attracted wide interest in Britain and in May 1768, King George III commissioned an expedition to find out.
It was the age of colonisation and Britain was not about to miss an opportunity to claim a new land to add to its already substantial empire.
There was even a convenient and benign explanation for this mission.
It was also the age of scientific discovery and the Royal Society - now the UK's national science academy - had petitioned the king to commission a voyage to Tahiti in the South Pacific to observe the transit of Venus.
This is where Venus passes between Earth and Sun, a rare but predictable event, with the potential to provide data on the distance from the Earth to the Sun and the size of the solar system.
The Royal Society wanted Dalrymple to lead this mission but the Admiralty prudently chose one of its own, James Cook, an officer skilled in cartography and navigation.
Cook, then 40, was promoted to Lieutenant and set sail from Plymouth aboard the bark HMS Endeavour in August 1768.
Aboard was a diverse complement of 94, comprising 73 sailors, Royal Marines for protection, an astronomer and high society botanist Joseph Banks who funded seven others to accompany him on the voyage. That included a pair of naturalists, two artists, a secretary and two black servants from his estate.
For such a long mission, Endeavour, a former collier specially purchased and refitted for this voyage, was tiny, just 30 metres. She was also slow, cruising around 15 km/h.
Cook was given two sets of secret orders, one for the voyage to the Pacific and one to be opened on departing Tahiti. However, this doesn't appear to have been a well-kept secret as details of the mission were reported in London and Paris newspapers even before he left.
Endeavour crossed the Atlantic, visited Rio de Janeiro to top up supplies, rounded Cape Horn and arrived at Tahiti in April 1769.
The transit of Venus was duly observed, though results weren't as good as expected, likely due to limitations of the instruments of the time.
Cook's sealed orders instructed him to search the south Pacific for the rumoured continent of Terra Australis, Latin for South Land, and he headed for New Zealand. He arrived on October 6, 1769 as just the second European mission known to have visited.
He remained until the end of March, mapping the coastline and raising the flag for England.
The locals weren't altogether friendly and a number died in clashes - a matter for regret, Cook wrote, as his instructions directed him to avoid hostilities.
He headed west. Cook himself was sceptical about the existence of the great southern continent but on April 19, 1770 sighted what is now southeastern Victoria.
Endeavour followed the coastline north, reaching a large shallow inlet. And on April 28, 1770 Cook and members of his party stepped ashore at what is now known as Botany Bay in New South Wales.
Undiscovered by Britain this new and different land may have been, but unoccupied it wasn't.
Cook's journal recorded encountering a pair of Aboriginal people, none too happy at the sudden arrival of a group of very strange foreigners. Warning muskets were fired and one was wounded but Cook did manage to avoid a larger confrontation.
Cook and Banks, delighted by the abundance of unique plants and animals, felt Botany Bay to be a suitable spot to establish a colony.
However, when the first fleet of settlers arrived 18 years later, it was to establish the new colony at Port Jackson, a much superior anchorage which Cook had noted on his charts but not explored.
Cook sailed north along the coastline, mapping as he went. He came close to disaster in mid-June when Endeavour was holed on the Great Barrier Reef, requiring seven weeks of repairs at what is now modern day Cooktown.
Finally, after reaching the far north, Cook landed on a small island - Possession Island - and raised the Union Jack, claiming the entire eastern coast of the continent for Britain.
That was despite his secret orders stating he should only do so with the consent of the native peoples. An enlightened directive, but Britain was going to claim this new territory regardless.
Cook returned to Britain on July 12, 1771, to the surprise of those who feared that Endeavour had been lost at sea or destroyed by the French.
His reputation as an explorer well established, Cook was to make two more voyages of discovery. He died in a confrontation with Hawaiian islanders in February 1779.
Australian Associated Press