300-year-old pirate-plundered shipwreck that once held 'eyewatering treasure' discovered off Madagascar

Archaeologists say they've found the submerged wreck of a sailing ship captured in 1721 near Madagascar, during one of history's most infamous pirate raids.

The American researchers, from the Center for Historic Shipwreck Preservation, have investigated the wreck for 16 years and now think it's the remains of Nossa Senhora do Cabo, a Portuguese ship carrying cargo from India that was attacked and seized by pirates, among them the notorious pirate captain Olivier "The Buzzard" Levasseur.

The wreck now lies on the floor of a small harbor on the island of Nosy Boraha off the northeast coast of Madagascar, which was a hangout known as Île Sainte-Marie during the "Golden Age of Piracy" in the early 18th century. New details of the investigations have been published in the latest issue of Wreckwatch magazine.

The identification of the wreck is "supported by multiple lines of evidence," the center's co-founder and director Brandon Clifford, one of the researchers, told Live Science in an email. These include analysis of the structure of the ship from its underwater remains, historical records and artifacts found in the wreckage.

Among them are devotional figurines and objects made from wood and ivory, including one that depicts Jesus' mother Mary; part of a crucifix; and an ivory plaque inscribed with gold letters that read "INRI." (According to the Christian gospels, these letters were inscribed by the Romans above the crucified Jesus and stood for "Jesus of Nazareth, King of the Jews" in Latin.)

The researchers think these artifacts were made in Goa, which was then the center of a Portuguese colony on India's west coast, and were being shipped to Lisbon in Portugal.

Related: 'Pirate' shipwrecks that sank in 1710 off Costa Rica are actually remains of Danish slave ships

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A sonar image of the seafloor shows the wreck thought to be that of Nossa Senhora do Cabo. Researchers think there are at least four pirate wrecks in the main harbor on the island of Nosy Boraha, off Madagascar.

A mosaic image of the harbor floor shows overlapping piles of ballast stones from ships' hulls. The ballast pile from Nossa Senhora do Cabo is at the right.

The island of Nosy Boraha off Madagascar's northeast coast was once a notorious hangout for European pirates known as Île Sainte-Marie.

Pirate raid

According to records, Nossa Senhora do Cabo (Portuguese for "Our Lady of the Cape") had left Goa early in 1721 bound for Lisbon, with the outgoing Portuguese viceroy and the Archbishop of Goa both on board.

But the vessel was attacked and captured by a group of pirate ships on April 8, 1721, near the French island of La Réunion (also known as Réunion Island) in the Indian Ocean.

The treasure it carried included ingots of gold and chests full of pearls, according to the researcher Denis Piat in his book "Pirates & Privateers in Mauritius" (Didier Millet, 2014).

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Artifacts recovered at the wreck site include gold coins inscribed with Arabic writing and pieces of fine porcelain.

The researchers have recovered several religious figurines and other devotional objects made from wood and ivory, presumably at Goa.

More than 3,300 artifacts have now been recovered from the wreck, but many others are still covered by sand and silt.

Clifford and his colleague Mark Agostini, an archaeologist at Brown University, said the Portuguese ship had already been badly damaged in a storm and had jettisoned most of its cannons to stay afloat; and so it was captured with little resistance.

The viceroy was eventually ransomed, but it's not known what became of the archbishop. About 200 enslaved people from Mozambique below decks, but there are no records of what happened to them.

According to Clifford and Agostini, the entire haul was "an eyewatering treasure, even by pirate standards," and the cargo alone may have been worth more than $138 million in today's money.

Sea dog base

The pirates then steered their captured prize toward Madagascar, about 400 miles (650 kilometers) west of La Réunion, to divide up their loot.

The researchers wrote that Île Sainte-Marie was chosen by European pirates because its sheltered anchorages were close to major shipping lanes. It was also known for its "absence of colonial governance," making it an ideal pirate base.

Clifford added that between seven and 10 shipwrecks were wrecked or scuttled near Île Sainte-Marie during the Golden Age of Piracy and "at least four pirate shipwrecks or their prizes lie in the harbor itself."

Agostini, meanwhile, told Live Science in an email that more than 3,300 artifacts had now been recovered from the wreck of Nossa Senhora do Cabo, but that the overlying silt and sand had made further recoveries difficult.

He added that archaeologists had previously overlooked Île Sainte-Marie and the scientific treasures it contained. "Ideally, future fieldwork will lead to more analysis of the many wrecks there," Agostini said.

Editor's note: This story was updated at 2:32 p.m. ET to remove a detail about a gold- and ruby-encrusted cross being on the ship at the time of its capture. This cross was mentioned in a book about the shipwreck, but Live Science has since learned that it might be a myth.