Saint-Aloüarn arrived at Dirk Hartog Island with two ships, having been separated from the rest of his squadron in the Indian Ocean. On 28 March he became the first European to formally take possession of any part of Western Australia. Two days later, at a cove the French named Baie de Prise de Possession, the Bay of Taking Possession, Mengaud led the ceremony ashore. Later mapmakers would rename it Turtle Bay, scrubbing the grand French intention from the chart. The Dutch had been bumping into this coast since 1616 and had decided it was worthless. The French were the first to plant a stake and say: ours. Then they sailed away, and nobody followed up. Louis XV had no appetite for a colony on the far side of the world, and the bottle was forgotten almost as soon as it was buried.

The story might have ended as a footnote, except the French were meticulous, and the dunes kept their secret. In 1998, more than two centuries later, a team led by Philippe Godard and Max Cramer searching Turtle Bay turned up a lead bottle cap with a coin embedded in it. The find electrified historians. The Western Australian Museum mounted a wider dig, and on 1 April 1998 archaeologists unearthed an intact bottle, sealed with an identical lead cap, an écu coin pressed into the metal exactly as the 18th-century records described. Two pieces of physical proof, drawn from the sand where Mengaud had left them, confirmed an event most people had never heard of. In 1999 a commemorative ceremony reburied bottles on the island, this time as memory rather than conquest.

Saint-Aloüarn's claim was only the opening move. Three decades later, Napoleon dispatched Nicolas Baudin with the corvettes Géographe and Naturaliste on a scientific expedition that spent seventy days mapping Shark Bay in 1801. Aboard were the naturalists François Péron and Charles-Alexandre Lesueur, the geographer Pierre Faure, and a young sub-lieutenant named Louis de Freycinet, who would later draw the first complete map of Australia. They charted nearly two-thirds of the continent's coastline and collected more than 2,500 species new to science. The historian Noelene Bloomfield titled her study of this era Almost a French Australia, and the name is no exaggeration. The British raced to claim the western coast partly because they feared the French would get there first.

The French lost the colony, but they kept the map. Roughly 260 places in Western Australia still carry names the explorers gave them. Cape Naturaliste and Geographe Bay are named for Baudin's ships. The Recherche Archipelago and D'Entrecasteaux honour an earlier French voyage. Péron, Lesueur, Freycinet, Leschenault, Faure, the men of the Baudin expedition left their surnames scattered across capes, estuaries, islands, and national parks. Many names that sound vaguely Dutch were in fact French inventions. Drive the Coral Coast today and you are reading, without realising it, the logbook of a nation that wanted this place and let it slip away. The flag never changed. The atlas never forgot.