The National Museum confirms: Shipwrecks in Costa Rica are Danish slave ships

For the first time, it has now been documented that two shipwrecks in Costa Rica are two named, Danish slave ships from the 18^th century.

This is revealed by scientific analyses from an underwater excavation in 2023, when marine archaeologists from the National Museum of Denmark and the Viking Ship Museum took samples of wood from one of the wrecks and from the bricks that were part of the cargo more than 300 years ago. Moreover, several clay pipes were found.

“The analyses are very convincing and we no longer have any doubts that these are the wrecks of the two Danish slave ships. 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 burnt,” says David Gregory, marine archaeologist and research professor at the National Museum of Denmark where he is head of the new maritime research centre Njord.

David Gregory led the excavations in Costa Rica together with the National Museum of Denmark’s marine archaeologist Andreas Kallmeyer Bloch, who has worked for several years to shed light on the origins of the ships.

“It’s been a long process and I’ve come close to giving up along the way, but this is 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. This provides two pieces that have been missing from the history of Denmark,” says Andreas Kallmeyer Bloch.

What the analyses show

Samples from the excavation have been analysed at the National Museum of Denmark and at the University of Southern Denmark, and they confirm what the historical sources say about the history of the ships.

Dendrochronological analyses (tree-ring dating) of oak wood from one of the wrecks show that the timbers originate in the western part of the Baltic Sea – an area that encompasses the north-eastern 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 wood is, moreover, charred and sooty, which confirms what historical sources say about one of the ships being set ablaze.

The bricks are of the same measurements as the so-called Flensburg bricks that were used in Denmark and in the Danish colonies. Analyses of the clay, carried out by Professor Emeritus Kaare Lund Rasmussen at the University of Southern Demark, show that the clay comes from Denmark – quite specifically from either Iller Strand or Egernsund. Both locations are situated by Flensburg Fjord which was, in the 18^th century, home to a sizeable brick-producing industry.

The clay pipes have been identified as ordinary, Dutch-produced pipes that were also used onboard Danish ships. The size, shape and patterns of the pipes suggest that they were produced in the period right before the ships became wrecked in 1710. Clay pipes were rarely used for more than five years.

The two slave ships

According to historical sources, the two Danish slave ships Fridericus Quartus and Christianus Quintus were shipwrecked off the coast of Central America in 1710. Fridericus Quartus was set ablaze, while Christianus Quintus had its anchor rope cut, following which the ship was wrecked in the surf. Until now, it has not been clear exactly where the ships were lost.

In Costa Rica, it has long been known that two wrecks were located in shallow waters off 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 yellow bricks were produced in Flensburg for use in Denmark and in the Danish colonies in the 18^th and 19^th centuries. In other European countries, other kinds of bricks and stones were in fashion when new buildings were erected.

The investigations are carried out jointly by the National Museums of Costa Rica and of Denmark, the Viking Ship Museum in Roskilde, the University of Southern Denmark, the Archaeological Commission of Costa Rica, the government body SINAC (Sistema Nacional de áreas de conservación Costa Rica) and Centro Comunitario de Buceo Embajadores y Embajadoras del Mar – a local NGO in Costa Rica.

The project falls under the National Museum’s new research centre Njord, which is planning to excavate several Danish shipwrecks abroad.

On the 28^th of April, the story of the two slave ships is told in the DR TV-programme Forsvundne Arvinger Special – Mysteriet om slaveskibene (Lost Heirs Special – the Mystery of the Slave Ships).

Contact: 

Andreas Kallmeyer Bloch, marine archaeologist and museum curator, the National Museum of Denmark, +45 5222 3608, ankb@natmus.dk  

Benjamin Asmussen, senior researcher of maritime history, the National Museum of Denmark, +45 4120 6034, beas@natmus.dk@natmus.dk  

David Gregory, marine archaeologist, research professor and leader of the maritime research centre Njord at the National Museum of Denmark, +45 4120 6473, djg@natmus.dk