In February 1694, British admiral Francis Wheeler set sail from the Bay of Gibraltar with an important mission. He was to bring a large sum of money to the Duke of Savoy in order to buy his loyalty and to ensure victory in Britain's ongoing war against France's Sun King Louis XIV.
But when the HMS Sussex arrived in the Strait of Gibraltar, it was hit by a violent storm and Wheeler struggled in vain to save it. The 50-metre warship went down with more than 500 men, 80 cannons and an estimated 10 tonnes of gold coins on board.
Three centuries later, a US company specialising in underwater treasure hunts, intends to haul up what is believed to be the world's richest sunken booty.
Florida-based Odyssey Marine Exploration has reached an agreement with the British and Spanish governments to explore a wreck it believes to be that of the Sussex at a depth of about 800 metres.
The value of the gold coins is estimated at up to €3.3 billion ($4.4 billion). If the treasure is found, it will be split between the explorers and the British government, the legal owner of the ship, which once sailed under its banner.
Not everyone is happy about the pioneering public-private deal, with some archaeologists fearing that the involvement of commercial companies could lead to a global scavenging of shipwrecks littering the world's oceans.
Odyssey, however, says it is committed to protecting the underwater cultural heritage and to developing a practical standard for commercial and academic coordination on shipwreck recovery.
Odyssey had already done exploration work on the wreck thought to be the Sussex, but was ordered to interrupt it in 2006 over Spanish fears that it was not respecting the conditions set by Madrid.
Archaeologists appointed by the Andalusian regional authorities will now participate in the operation, and the central government also pledged to keep a watchful eye over it to prevent any archaeological "pillaging" on Spanish territory.
It is actually unclear whether the wreck is in Spanish waters but Madrid wants to make the rules clear in view of possible explorations of Spanish wrecks later on.
Spain is believed to be one of the world's richest underwater treasure houses. More than 700 wrecks dating from the 16th to the 19th centuries are estimated to lie in its waters, many of them possibly loaded with gold and silver plundered in Latin America.
"There is more gold in the Gulf of Cadiz than in the Spanish national bank," archaeology professor Manuel Martin Bueno said.
There is also the possibility that the wreck located by Odyssey is not the Sussex, but a Spanish galleon, another reason why Madrid wants to keep its explorers under control.
Odyssey Marine Exploration scanned about 1,000 square km of sea bottom with sonars in its search for the Sussex.
It located 418 wrecks and other targets, only one of which contained cannon. It was positioned near to where the Sussex reportedly foundered.
The site is too deep for divers, but Odyssey intended to use search and recovery vessels, side scan sonar equipment and robots, the company told DPA.
Odyssey has formerly found several treasures, including gold coins and artefacts worth $75 million off the US coast in 2003.
The length of the new exploration depends on many factors and cannot yet be determined, company sources said.