Medieval Cog: The Ship That Made Ports Boom

A Cog of Unprecedented Size

Historically, the cog was the workhorse of northern trade. Developed around the 10th or 11th century, the cog was a clinker-built (overlapping-plank) vessel with a single square sail and a stern-mounted rudder. Its boxy hull, often featuring a high bow and stern castles, provided it with enormous cargo volume. For hundreds of years, the cog carried the bulk of Hanseatic commerce: cloth, wine, and spices from the West; grain, wood, resin, salt, and fish from the Baltic. By the 13th century, it was the emblematic ship of the Hanseatic League, depicted on city seals and even coats of arms. (Several medieval cogs have been found or exhibited, the most famous being the Bremen cog of 1380, now at the German Maritime Museum.) But none was as large as Svælget 2. 

The Bremen Cog at German Maritime Museum, 2021

The Bremen cog, shown here in Bremerhaven, could carry about 125 tons of cargo. By contrast, Svælget 2’s 300-ton capacity makes it a true super-ship of its era. Archaeologists found that the wreck included remains of both bow and stern castles – timber platforms depicted in medieval drawings but never before discovered in an actual cog. This is the first archaeological proof that large cogs really did have the high wooden shelters above deck long shown in manuscripts. In Svælget 2, extensive timbers from a covered stern deck have been preserved. As Otto Uldum explains, finding this “gives us an opportunity to say something entirely new about how cogs were equipped for sailing”. Similarly, in the bow of the wreck, archaeologists uncovered the earliest example of a brick-lined galley (cooking hearth) in any Danish medieval ship. A hearth with about 200 bricks once allowed sailors to prepare hot meals on board – a luxury compared to the cold, dried provisions that sailors usually ate. Around the galley, the team found bronze pots, ceramic bowls, fish and meat remains, and even hundreds of split “sticks” likely used for preparing stockfish.

The rigging of Svælget 2 was also exceptionally well preserved. Because the ship lay buried in sand, archaeologists lifted dozens of ropes, blocks and chains – an unprecedented haul of medieval cordage. Rigging is crucial on a square-rigged ship since it holds the mast and controls the sail. Otto Uldum notes that by studying these ropes, “we can say something entirely new about how cogs were equipped for sailing.” In short, Svælget 2 is a treasure trove of 15th-century ship technology. Its iron fastenings, wooden planks and even paint fragments will help researchers understand construction techniques that have been lost for centuries.

Yet Svælget 2 was not a warship. No weapons or military gear were found – instead, the small artefacts tell the story of daily life on board. Personal items like painted wooden dishes, leather shoes, combs and prayer beads were recovered. One hopes the 15th-century sailor on this voyage was a devout man: among the finds were at least two rosary beads. From these everyday treasures, we glimpse a “transfer of life at sea from life on land”, as Uldum puts it.

Timber Trade and Shipbuilding Networks

Dendrochronological analysis of the hull timbers provides a snapshot of international trade in 1410. The oak planks came from Pomerania (modern-day Poland), while the ship’s frames (ribs) were cut from wood in the Netherlands. This combination suggests a complex supply chain: heavy, prime oak for the hull was floated from the forests of the southeast Baltic to Dutch shipyards, while local carpenters in Holland finished the build. “It tells us that timber exports went from Pomerania to the Netherlands,” Uldum explains, “and that the ship was built in the Netherlands, where the expertise to construct these very large cogs was found.” Thus, Svælget 2 embodies late-medieval North Sea–Baltic cooperation: raw materials from the East Baltic and skilled craftsmen in the Low Countries, all in the service of Northern Europe’s booming maritime economy.

In fact, the Netherlands was already turning into a maritime heavyweight in the early 15th century. Historians note that around 1400, large Dutch fleets crossed the North Sea to fetch grain and Baltic goods. By the end of the century, Dutch merchants were even bypassing the Hanseatic middlemen, buying grain directly in the Baltic and exporting salt and other wares westward. The Svælget 2 reflects this turning point: a huge Dutch-built cog, operating in the Øresund, points to the era when the great Northern Network of trade was becoming more international and trade volume was surging.

The Age of Bulk Trade

What exactly was Svælget 2 carrying? Paradoxically, the wreck itself reveals nothing about its cargo – most of the trade goods are long gone. The hold of the cog had no covering, so when it sank, any loose cargo would have floated away or drifted off. No barrels, crates or chests of goods remain. The missing ballast also suggests the ship was heavily laden when she sank – she had no extra stone weight because her hold was already full of commerce. What might that commerce have been? Otto Uldum speculates that “to transport bulky cargo – salt, timber, bricks or basic food items”. Indeed, other sources on Northern trade confirm that these were exactly the kinds of goods moving through the Øresund and Baltic then. Cities like Lübeck and Danzig imported salt (e.g., Lüneburg salt from the south), timber and wood products (mast and plank timber from Pomerania), grain (rye and wheat from Prussia/Livonia), iron from Sweden and Poland, and staples like herring and beer. Small wonder that excavators mention “everyday goods” when describing the cog’s mission – by the 15th century, cogs weren’t reserved for luxury trade but were ferries of bulk commodities, ferrying the needs of a growing population.

This shift from luxury to bulk was one of the hallmarks of the late Hanseatic era. In earlier medieval times, long-distance trade focused on cloth, spices and the like. But by the 14th–15th centuries, improvements in shipbuilding and navigation – and a rising population – meant that ordinary foodstuffs and building materials could travel far across the continent. In fact, Europe’s population exploded from some 18 million in the 7th century to over 70 million by the 14th century. More people meant more mouths to feed and more houses to build, and the Hanseatic cog was the perfect vehicle. A large cog like Svælget 2 embodied this “economic revolution” – it hauled bricks, salt, timber and fish that ordinary people used every day, not just the silks and spices of the elite.

Life on Board and Legacy

Finally, Svælget 2 offers a touching window into life aboard a medieval merchant ship. The myriad small finds – combs, plates, a cooking pot – allow us to imagine a sailor’s routine: waking before dawn to stoke the brick oven, rations of salt cod (from stockfish sticks) laid out on wooden bowls, a sailor saying prayers with his rosary before setting sail at dusk. These personal traces, preserved by sand for six centuries, humanise the story of Hanseatic commerce.

The wreck of Svælget 2 has captured the public imagination (a Danish TV documentary, Mystery in the Deep, is already in production). Scholars, meanwhile, are humbled: this ship is a concrete “piece of the puzzle” that will let researchers calibrate medieval trade and technology. It shows unambiguously that cog construction could scale up to near 300 tons and still be managed by a crew of fishermen-turned-sailors. The Dutch and Scandinavian shipbuilders had truly tested the limits of their craft.

In sum, the Medieval Cog discovered at Lynetteholm rewrites a chapter of Northern European history. It bridges legends and facts: we had drawings and sagas of galleons with castles on deck, but now we have the real thing. It underscores the interconnectedness of Hanseatic Europe – from Pomeranian forests to Dutch shipyards to Danish waters – and the lengths to which medieval societies would go to feed their markets. For history enthusiasts, Svælget 2 is a reminder that sometimes the silent sea still holds surprises that reshape how we see the past.