The world’s largest medieval cog has been identified on the seabed in the Øresund strait off Copenhagen, a discovery that Danish researchers say offers rare new evidence about late-medieval shipbuilding and everyday life at sea. The 28-metre shipwreck—named Svælget 2—was found between Amager and Saltholm during preliminary seabed surveys linked to Copenhagen’s major coastal development project Lynetteholm, and has been dated to around 1410.
Where Svælget 2 was found in the Øresund shipping lane
The wreck was located in the sailing channel known as Svælget, in the Øresund between Amager and Saltholm, at a depth of roughly 13 metres. According to the Viking Ship Museum (Vikingeskibsmuseet) in Roskilde, the site’s conditions helped preserve the ship’s starboard side from keel to rail, an unusually complete section for a wreck of this period.
The ship has been measured at about 28 metres long, up to 9 metres wide, and around 6 metres high. Researchers estimate it could carry about 300 tonnes of cargo—significantly larger than other known medieval cogs.
Why the world’s largest medieval cog is a milestone for research
Marine archaeologist (marinarkæolog) Otto Uldum, who led the excavation, described the find as a “milestone” for maritime archaeology because it provides a concrete reference point for how the biggest merchant vessels of the period were built and equipped. For researchers, the ship’s scale matters as much as its preservation: it suggests that late-medieval trade in Northern Europe relied on vessels capable of moving large volumes of everyday goods efficiently.
In practical terms, a cargo capacity on this scale implies organised commercial networks, predictable demand, and financial structures able to fund construction and operation of very large ships. That, in turn, helps explain how maritime trade reshaped the economies of the North Sea, Øresund and Baltic regions in the 1400s.
What the ship can tell us about trade routes in Northern Europe
Cogs were developed in the North Sea area and became the backbone of medieval commerce, linking ports in what are now the Netherlands, Denmark, Sweden, Germany, Poland and the wider Baltic world. The museum notes that large cogs were built to make demanding voyages—such as sailing around Skagen—to reach Øresund and the trading towns of the Baltic.
Dendrochronological analysis indicates Svælget 2 was built around 1410 with timber from two regions: Pomerania (in today’s Poland) for planking, and the Netherlands for the frames. The mix points to long-distance supply chains even for heavy materials like ship timber, and supports the conclusion that the ship was built in the Netherlands.
Rigging, “castles” and a brick galley found on board
Researchers report that Svælget 2 includes preserved features rarely documented archaeologically in such detail.
- Rigging details: a substantial set of rigging elements, including a reported set of 16 deadeyes (jomfruer), which could help researchers reconstruct how the largest cogs handled sail control and mast support.
- Castles: remains linked to the cog’s fore and aft “castles” (raised structures), long depicted in drawings but seldom confirmed through surviving structural evidence.
- A brick-built galley: evidence of a masonry cooking area with bricks and tiles, described by researchers as among the earliest examples of its kind in Danish waters, suggesting a higher level of onboard organisation and the ability to prepare hot meals.
Personal items, but no clear trace of the cargo
Archaeologists recovered a range of personal belongings and everyday objects—reported examples include bronze cooking pots, ceramic vessels, shoes, combs, and rosary beads. Those finds provide a rare window into the routines and material culture of a merchant crew.
At the same time, the ship’s cargo remains uncertain. The museum reports no confirmed traces of the load, a gap researchers explain by pointing to the likely openness of the cargo hold: items such as timber, textiles or barrels of salt could have floated away during the sinking.
The Lynetteholm link and the cost of seabed surveys
The discovery is tied to the large-scale Lynetteholm project, an artificial coastal extension intended to support long-term storm-surge protection and future urban development in Copenhagen. As part of the preparatory works, seabed areas and sailing routes have required extensive investigation.
The marine archaeological work and associated surveys connected to Lynetteholm have been reported at DKK 150 million (about €20.1 million). The museum says the excavation was financed by By & Havn, the public development company responsible for the project.
What happens next: conservation, research and a documentary series
Salvaged ship parts are being conserved at the National Museum of Denmark (Nationalmuseet) facility in Brede, while researchers continue to document and analyse the structure and finds.
The discovery will also be featured in a DR documentary series, Gåden i dybet, which follows the underwater excavation and subsequent research questions—such as what caused the sinking and who sailed on board. The museum notes that several of those questions remain open, and that further scientific work is expected to refine the interpretation of the ship’s final voyage.
In a Nordic and European perspective, Svælget 2 offers tangible evidence of the trade systems that bound Northern Europe together centuries before modern economic integration—showing how maritime logistics, standardised ship types and cross-border supply chains already shaped the region’s shared history.
