Marine archaeologist and research professor David Gregory from the National Museum of Denmark at piled bricks on the seabed in Costa Rica.
Jakob Olling/The National Museum of Denmark

Two 18th-century shipwrecks off the coast of Costa Rica, previously thought to have been pirate ships, have been confirmed to be two Danish slave ships, a museum said Sunday.

"Investigations of ship timbers, bricks from the cargo and clay pipes found during underwater excavations" had determined the identity of two vessels shipwrecked in 1710, Denmark's National Museum said in a statement.

Marine archaeologists identified the slave ships Fridericus Quartus and Christianus Quintus, which, according to historical sources, were wrecked off the coast of Central America in 1710, said the museum. The museum also released images of Andreas Kallmeyer Bloch and David Gregory digging underwater and excavating bricks and wood from the wreckage.

Fridericus Quartus was set on fire, while Christianus Quintus was wrecked in the surf after its anchor line was cut. Until now, it has not been clear exactly where the ships were lost.

The museum added that in Costa Rica, it had long been known that two wrecks were located in the waters of the Cahuita National Park.

"For many years, however, they were thought to be pirate ships. But when American marine archaeologists in 2015 found yellow bricks in one of the wrecks, new questions emerged about the history of the ships," the museum said.

An underwater excavation was carried out in 2023. It was part of the National Museum's new research center, Njord, which the museum said is planning to excavate several Danish shipwrecks abroad.

"The analyses are very convincing and we no longer have any doubts that these are the wrecks of the two Danish slave ships," Gregory, a research professor at Denmark's National Museum, said in the statement.

"The bricks are Danish and the same goes for the timbers, which are additionally charred and sooty from a fire. This fits perfectly with the historical accounts stating that one of the ships burned," Gregory added.

Fellow marine archaeologist Bloch, who's also a museum curator, called it "undoubtedly the craziest archaeological excavation I've yet been part of."

"Not only because it matters greatly to the local population, but also because it's one of the most dramatic shipwrecks in the history of Denmark, and now we know exactly where it happened," the marine archaeologist said.

The Danish government banned the transatlantic slave trade in 1792, but the country didn't abolish slavery until half a century later, in 1847, according to the museum.

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