A Hanseatic-era cog buried beneath Tallinn’s Lootsi Street since the 1360s has been dated through tree-ring analysis to oak forests across northern Poland and the Tallinn hinterland, with one cluster of hull planks matching timber still hanging in the door of the city’s medieval Bremen Tower. That is according to a new study published in the Journal of Cultural Heritage, which confirmed the vessel as one of the largest medieval shipwrecks recovered in Europe.
Construction crews working on the foundations for a new office building struck wood roughly 1.5 metres below ground on 31 March 2022, exposing the timber hull of a 14th-century merchant vessel measuring 24.5 metres long, 9 metres wide, and 4 metres tall. Engineers later cut the hull into four sections to clear the development site, requiring 3 months of preparation and 13 hours of transport to relocate the wreck for conservation.
Tree-ring analysis across multiple plank groups from the hull showed that most of the oak matched timber sources in northern Poland — the standard supply chain for Hanseatic shipbuilding in the era. One cluster of planks did not fit that pattern, with growth rings matching a sequence found in a door still hanging in Tallinn’s medieval city wall, wood previously linked to the Tallinn hinterland or western Lithuania.
The matched timber sequence has prompted researchers to ask whether the cog was assembled in western Lithuania and completed for its first voyage from Tallinn before sinking near the harbour, with the study stopping short of a firm conclusion. Sourcing hulls from multiple regions was standard practice for large Baltic shipbuilding of the period, with the Hanseatic League’s commercial reach pulling oak across thousands of kilometres of coastline into yards from Lübeck to Riga.
Several structural features have resisted the cog classification since the excavation began, with the hull sealed in pitch-covered animal fur alongside the moss caulking standard for cogs of the period. Certain plank configurations had been believed to appear in shipbuilding only a century later, prompting Estonian Maritime Museum archaeology researcher Priit Lätti to consult specialists abroad without finding a comparable wreck.
The state of the ship’s interior pointed to a sudden sinking rather than a planned abandonment, with tools, weapons, and worn leather shoes scattered through the hold and two well-preserved ship rats recovered from the wreck. “People had to get off the ship in a hurry,” Lätti said, with the inventory ruling out a controlled scuttling.
Among the most striking artefacts recovered from the wreck is a dry compass reported by Estonian public broadcaster ERR as the oldest surviving example of its kind in Europe, with the magnetised needle still pivoting freely after more than six centuries underwater. It comes as Wood Central reported on the discovery of 1,200-year-old ship timber from the Frankish empire’s Dorestad trading port in March 2026, where Carolingian-era oak surfaced during sewer works in Wijk bij Duurstede.
An even older wreck sits buried nearby and has not been touched, with Lätti confirming the ground has preserved the timber for centuries, and that better excavation methods may eventually allow a more complete recovery. The Lootsi cog is scheduled for permanent public display at the Estonian Maritime Museum once Finnish conservators and the museum team complete moisture-controlled stabilisation of the four-section hull.
For more information: Daly, A., Sohar, K., Läänelaid, A., Lätti, P., & Reinvars, L. (2026). Timber for a medieval Cog – Wood studies of the Lootsi 8 wreck, Tallinn. Dendrochronologia, 97, Article 126519. https://doi.org/10.1016/j.dendro.2026.126519
