Haunting slave ships found off coast of national park 300 years later: 'Very convincing'

The ships, named Fridericus Quartus and Christianus Quintus, are located in shallow waters off Costa Rica's Cahuita National Park. The 18th-century vessels were shipwrecked in 1710, according to the National Museum of Denmark.

"Fridericus Quartus was set ablaze, while Christianus Quintus had its anchor rope cut, following which the ship was wrecked in the surf," the museum's press release noted. "Until now, it has not been clear exactly where the ships were lost."

Pictures show divers carefully examining the shipwreck, which shows signs of significant decay from the past 315 years.

Though the ships were excavated in 2023, researchers didn't know that they were slave ships until recently. The vessels were long believed to be pirate ships.

The excavation involved, in part, taking samples from the wood of the ships, as well as yellow bricks that were part of the ship's cargo. 

Researchers also conducted dendrochronological analyses - tree-ring dating - to determine where the wood came from. They found it came from Northern Europe.

"The timbers originate in the western part of the Baltic Sea, an area that encompasses the northeastern German province of Mecklenburg, as well as Schleswig-Holstein, Denmark and Scania - and that the tree was cut down sometime during the years 1690-1695," the release said. 

"The wood is, moreover, charred and sooty, which confirms what historical sources say about one of the ships being set ablaze."

"The size, shape and patterns of the pipes suggest that they were produced in the period right before the ships became wrecked in 1710," the press release added. "Clay pipes were rarely used for more than five years."

"In other European countries, other kinds of bricks and stones were in fashion when new buildings were erected," the museum said.

"Both locations are situated by Flensburg Fjord, which was, in the 18th century, home to a sizeable brick-producing industry."

After samples from the excavation were analyzed at the National Museum of Denmark and the University of Southern Denmark, researchers concluded the findings corroborate what historical sources say about the history of the ships.

David Gregory, a marine archaeologist at the National Museum of Denmark, said that the results fit "perfectly" with historical accounts about one of the ships burning.

"The analyses are very convincing and we no longer have any doubts that these are the wrecks of the two Danish slave ships," Gregory said. 

National Museum of Denmark marine archaeologist Andreas Kallmeyer Bloch said he'd "come close to giving up" during the long research process - but is stunned by the results.

"This is undoubtedly the craziest archaeological excavation I've yet been part of," Bach said. 

"This provides two pieces that have been missing from the history of Denmark."

Fox News Digital reached out to the National Museum of Denmark for additional information.