From the time Columbus discovered the New World in 1492, Spain transported goods and treasure across the Atlantic, and after the conquests of Mexico, Panama, Colombia, and Peru, Spanish ships carried gold, silver, emeralds, and other riches back to Spain. To defend this trade against English, French, and Dutch privateers and pirates, treasure fleets were organized as early as 1537 and operated as convoys of numerous ships escorted by armed galleons. Twice each year they sailed from Spain to the New World with colonizers, tools, and scarce goods, then returned from ports in Central and South America carrying precious metals, gems, sugar, tobacco, spices, pearls, silk, lumber, and agricultural products, gathering in Havana to take on water, food, and supplies for the six-to-eight week voyage to Spain. This system continued until 1790, but jagged reefs, poor charts, inexperienced sailors, storms, and hurricanes posed constant danger. Fontenada wrote of the fleet wrecked in 1553, when some ships smashed along the Keys and others were blown back into the Gulf of Mexico, and in 1554 four of fifteen ships were lost on the coast of Florida. On September 4, 1622, a fleet of 28 ships left Havana, encountered a hurricane in the Florida Straits, and by September 6 eight ships had sunk between the Marquesas Keys and the Dry Tortugas. Among them was the Nuestra Señora de Atocha, the admiral's ship, 112 feet long, rated at 550 tons, armed with 20 bronze cannons, and laden with 24 tons of silver bars, 180,000 pesos in silver coins, 125 gold bars or discs, 1,200 pounds of worked silverware, gold chains, emeralds, and jewelry; only five of the 265 people aboard survived. In 1985 Mel Fisher discovered the Atocha and over several years salvaged more than 500 million dollars in treasure, some of which can be seen at the Mel Fisher Maritime Museum in Key West. On July 24, 1715, another treasure fleet sailed from Havana with twelve ships, and a hurricane on the morning of July 31 sank eleven of them off the coast of Florida, costing as many as 1,000 or more lives. On July 13, 1733, the New Spain Treasure Fleet of 21 ships, commanded by Lt. Gen. Don Rodrigo de Torres in his flagship El Rubi, a 60-cannon galleon carrying more than 2,000 boxes of gold and silver coins, was struck by a hurricane on July 15 that destroyed the fleet and scattered it from Elliott Key to Marathon, about 80 miles. Four ships were later refloated and repaired, but after Spanish salvage efforts ended the wrecks lay undisturbed for more than 200 years until 1938, when local diver Art McKee was shown a ballast pile off Plantation Key, researched the site, found a Spanish map showing locations of the 1773 Treasure Fleet, identified the ship as the Capitana, and over years recovered silver, gold, jewelry, cannons, and many artifacts, enough to build McKee's Museum of Sunken Treasure on Plantation Key.