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Recent Discoveries

The medieval shipwreck from Kalverev Syd, Denmark

Mikkel H. Thomsen
p. 187-192


Avant la construction d’un nouveau pont sur le détroit de Storstrømmen, le Musée des Navires Vikings de Roskilde a été amené à fouiller une partie d’un navire construit à clin, daté dendrochronologiquement vers 1250‑1255 apr. J.-C., et pourvu d’un système d’étanchéité externe constitué de lattes et de sintels. La découverte a été documentée in situ par la photogrammétrie 3D et par la suite récupérée pour une documentation par balayage laser 3D et pour sa conservation. Cet article présente les rares vestiges du navire et les replace dans le contexte des traditions de construction navale médiévales telles qu’elles sont actuellement connues. Un programme complet d’analyses scientifiques donne un aperçu de la vie à bord et peut-être même de l’organisation des différents espaces de chargement du navire.

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Texte intégral

1. Site history and recording methodology

1The shipwreck presented here was identified during archaeological surveys ahead of the construction of a new rail and road bridge across the Storstrømmen sound between the Danish islands of Masnedø and Falster (fig. 1).

2It was found on the south bank of the shallow reef Kalverev where it lay covered by up to 1.5 m of sediment – on top of which lay a modern wreck. It was only discovered because the area was also suspected to hold Stone Age remains on a fossil terrain even deeper in the sediment. It was during a mechanical test excavation targeting these remains (and in the process removing the modern wreck) that medieval ship timbers were dug up. As it turned out, the wreck physically obstructed the intended construction works, necessitating full excavation, investigation, and removal (Thomsen 2017). This planned destruction of the site necessitated a particular focus on detailed and accurate documentation, as well as the fullest possible harvesting of information, in order to best preserve the research potential of the site.

Fig. 1: Location of the wreck site in the Storstrømmen sound

Fig. 1: Location of the wreck site in the Storstrømmen sound

(drawing M. Thomsen)

3The wreck was recorded in situ using 3D photogrammetry controlled by a trilateration network, key points of which were georeferenced by means of RTK-GPS survey.

4Later, the salvaged parts were recorded individually using 3D laser scanning in combination with contact digitising of features not readily visible or identifiable in the scanned surface.

  • 1  The site history and methodology is described in a forthcoming publication by Matko Čvrljak and th (...)

5Thirdly, as much environmental evidence as possible was secured for subsequent analysis.1

2. Vessel remains

6As it turned out, a lot of features of the wreck proved to be illustrative of developments in medieval shipbuilding, making it suitable for future museum display, education, and dissemi­nation. Therefore it was decided to conserve and keep the timbers (and the waterproofing material), and they are currently undergoing conservation treatment at the National Museum of Denmark.

7The wreck remains, dated to circa AD 1250–1255 (Daly 2017), constitute the aft end of the port side of the bottom of a clinker-built ship made entirely of oak (Quercus sp.) timbers and iron rivets. Planks are preserved from the fifth or possibly sixth (loose) port strake over the keel to the second starboard strake (fig. 2).

8Four floor timbers are partly preserved and the positions of a further eleven are evident from treenails and from impressions in the tar conglomerate covering the inboard face of the planking. It is currently thought that the preserved remains span from the sternpost to somewhere just ahead of midships.

Fig. 2: Site plan: photogrammetry overlaid with traced timbers and frame stations

Fig. 2: Site plan: photogrammetry overlaid with traced timbers and frame stations

(photogrammetry M. Čvrljak, drawing M. Thomsen)

2.1. Construction

9The ship was built on a seemingly straight, (presumably double-) tapered keel with a marked T-shaped cross section. To this, plank strakes were attached with round-shafted iron clinker nails, circa 6.5 mm in shaft diameter, and square-to-rhombic roves. The planks were of varying length, up to 34 cm wide and circa 2 cm thick, radially cleft, and of relatively good quality although somewhat crudely finished. A single, short length of plank seems to have been replaced during the original construction phase, after which only routine overhaul, in the form of surplus clinker nails, is evident. Individual planks were joined in relatively long oblique scarfs (up to circa 19 cm), although without the protruding “ledge” typical of the high/late medieval, long plank scarf (Bill 1995, p. 200, fig. 3) The scarfs were waterproofed with a wad of wool and assembled with iron clinker nails.

10The plank seams were waterproofed by an inlaid, usually Z-spun, strand of medium-coarse wool/animal hair during assembly, supplemented on the outside by a strand of Spaghnum cuspidatum moss (Petersen A. H. 2018). The latter could either have been laid in during construction or driven in after plank assembly. This was held in place on the outboard side by a narrow waterproofing lath of oak (Baittinger 2018) with lentil-­shaped cross section, secured with iron sintels. Judging from the odd rust impression here and there, the sintels were of Vlierman’s type B/C (Vlierman 1996, p. 55, fig. 25, p. 58, table II). Their lower leg was driven approximately halfway through the thickness of the lower plank and their upper leg directly into the narrow edge of the upper plank.

11Three preserved aft hood ends reveal the angle and relative position of the preserved lower part of the sternpost, even if its direct connection to the keel is missing. The keel terminates aft in a simple vertical scarf, and the lower end of the sternpost is broken just at the heel, not revealing whether it was in effect a long stern knee extending forward all the way to the keel scarf or whether there was a separate section of keel in between. On the better preserved downward-facing port side of the sternpost it can be observed that the lowest four strakes terminated in a stepped rabbet, whereas the upper strakes spanned the entire face of the triangular post.

12The floor timbers, almost square in cross section, were ­connected to the hull planks with treenails and to now missing futtocks in a simple horizontal scarf. Their spacing is regular, circa 50 cm, except for the section aft of frame station 13 (fig. 2).

13There were no preserved traces of keelson, stringers, ceiling or any other internal timbers.

2.2. Building tradition

14All in all the remains bear a striking resemblance to Wreck I from Slottsfjärden, Kalmar, Sweden, excavated by Harald Åkerlund in the 1930s. The Kalverev Syd vessel, though proba­bly some 10% bigger, has the same keel and sternpost shape, hood end fastening, framing pattern, and probably also a similar afterdeck arrangement, including the irregular frame spacing underneath (Åkerlund 1951, p. 27–50, pls 4–9). The waterproofing method, however, seems to differ.

15Many of these features have in the past been regarded as chronological or geographical markers or as markers of a certain technological paradigm. In our current understanding the vessel places itself neatly in the chronology of the so-called Nordic clinker-building tradition, the development of which has been laid out rather convincingly by Jan Bill (1995).

16Some features, such as the T-shaped keel, the majority of long planks, the plank width and conversion, and the ironwork are traditionally thought of as “archaic” for the mid-13th century, whereas others, such as the crude plank finish, the scarfs, the framing system and (with some caution, as this feature is rarely preserved in typical shipwrecks) the sternpost assembly point to changes happening gradually through the 12th to 14th century (Bill 1995, p. 198–202).

17So, the vessel was in many ways a truly “contemporary” Nordic clinker-ship, however, the waterproofing method seems to be the odd exception. In Scandinavia, this method is usually associated with the so-called cog (or bottom-based) building tradition. The same can be said for the use of moss as waterproofing material (although south of the Baltic Sea it was also commonly used in wholly clinker-built vessels).

18This begs the question: what is a “tradition”? And how do traditions interact? Through transfer or through assimilation? And should we regard the development of clinker shipbuilding as a gradual progression, or is there room for regression and diversification? And what drives the changes? Is it the commodi­ties traded? The trade routes and waters? Or is it profit, as implied in Bill’s 1995 title?

2.3. Date and provenance

19Central to this question is, of course, the timber provenance of the ship. This, however, is not entirely clear.

20Two of the ten datable dendrochronological samples (representing seven individual trees) have a clear match with South Jutland chronologies, whereas the remainder match east and west Danish chronologies equally well (Daly 2017). If this reflects procurement of timber from non-local sources in the 13th century it is highly interesting in its own right, but for the purpose of investigating building traditions it will suffice to say that the ship was Danish built. Did the seemingly uncommon waterproofing method come along with building materials from South Jutland – the same region as the dendro-provenance of early cogs (e.g. Hocker, Daly 2006; Daly 2015)? Or did it flow into the Nordic clinker paradigm from trade partners south of the Baltic?

3. Environmental remains

21In order to investigate this last question further it would be convenient if the wreck presented some clues to its past cargo and other remains of life on board. While there is not a single artefact found in the wreck, we are lucky that, on a microscopic level, a layer accumulating environmental evidence throughout the ship’s ­construction and operation is preserved: namely a thick conglomerate of tar, sand, wood chips and also micro- and macrofossils adhering to the inside faces of the hull planks (Henriksen et al. 2018).

22The conglomerate is clearly visible as a yellowish substance terminating, in the port side, rather abruptly at frame station 9, whereas it continues at least to frame station 12 in the starboard side. The extent of the conglomerate may be an indication of the cargo hold. Another such clue is the frame spacing mentioned above, indicating, perhaps, that a deck existed aft of frame ­station 13 (fig. 2).

3.1. Botanical micro- and macrofossils

23The botanical macrofossils, summarised in fig. 3, seem to confirm a functional distinction between the area with massive conglomerate and the presumed decked area: cereals and other edible plants are only present forward of frame station 13 (additionally, aft of frame station 15 even field weeds – a possible proxy for cereals – disappear from the record). The apparent absence of conglomerate in the port side between frame station 9 and 13 cannot be explained through similar analysis due to the very scarcity of sample material. It would have been intriguing to know if perhaps there was a longitudinal functional division of this part of the ship. Was it, for example, kept clear of cargo to maintain access to the area below the afterdeck?

Fig. 3: Distribution of botanical macrofossils

Fig. 3: Distribution of botanical macrofossils

(drawing M. Thomsen after data from Henriksen et al. 2018)

24Besides being clues to the ship’s arrangement, the macro­fossils also provide an indication of activities on board and cargo carried. The general picture is of a ship carrying agri­cultural products, but what is perhaps more interesting is that they seem to have been unprocessed. Rye (Secale cereale), for example, was carried not just as threshed grains but also including the ears of the plant, indicating that the rye was transported as sheaves, inefficient as it may seem. The same was most likely the case for barley (Hordeum vulgare), as suggested by pollen analysis. Barley self-pollenates, leaving the pollen inside the chaff until threshing, so the presence of barley pollen indicates that the grain was transported before threshing. Also, hay may have been carried this way. Other pro­ducts include bog myrtle (Myrica gale) and hemp (Cannabis sativa) or, more unlikely, male hops (Humulus lupulus). Incidentally, all of these products appear on lists of various forms of tax, duty or tithe from the medieval period (Porsmose 1988, p. 307–314).

25Other botanical specimens are thought to be the remains of food supply onboard: apple (Malus sp.), raspberry (Rubus idaeus) and elderberry (Sambucus nigra) seeds, and – most conspicuous – a large number of humanly cracked hazelnut (Corylus avellana) shells.

3.2. Zoological macrofossils

26The macrofossils also contained a variety of zoological specimens, mainly insects (Petersen J. 2018a, 2018b). Not only do they support the botanical evidence for the transport of grain, but the majority of specimens are actually associated with livestock, living in either the pastures or the dung (in which case the aforementioned hay and rye may be interpreted as fodder for the voyage).

27The dark mealworm beetle (Tenebrio obscurus) is an example of the former, but it may also serve as an indication that the many down and feather fragments also found in the conglomerate are indeed from live animals carried on board at times and not just debris blown into the wet tar by the spring winds.

28The dung beetle (Aphodius sphacelatus) – along with flies (e.g. Scathophaga stercoraria) – is perhaps the best-known example of the latter.

29Also powderpost beetles (Lyctus linearis) were found. As no traces of their so-called shot holes (from which the larvae emerge) are found in the ship timbers, the vessel was almost certainly at times engaged in the transport of firewood – another major shipping commodity during the pre-industrial era. Firewood may also explain the presence of a few bones from the least weasel (Mustela nivalis), wood piles being one of its preferred habitats.

30It should be noted that the zoological evidence is somewhat conjectural and should mostly be seen in conjunction with other evidence. Some species may reflect more than one habitat, in which case all habitats are represented in fig. 4. Furthermore, one individual may be destroyed and the parts dispersed, resulting in more than one specimen per individual. Last but not least, the small sample volume naturally affects the statistical significance of the results.

Fig. 4: Distribution of insects by habitat

Fig. 4: Distribution of insects by habitat

(drawing M. Thomsen after data from Petersen, J. 2018a)

31This being said, it may still be possible to observe distribution patterns. Samples with species relating to animal dung (habitats Pasture_dung and Indicators_dung in fig. 4) are – except for one single fly pupa in a sample taken underneath frame 3 – confined to the area between frame stations 6 and 12, supporting the botani­cal and constructional evidence for an afterdeck but maybe even indicating a sub-division of the cargo hold. Frame 6 is currently suspected to be the midship frame as it is the central of three frame stations marked with incisions on the top face of the keel (figs 2–4). If the cargo hold was indeed divided in two compartments, the midship frame would be a likely place to divide it.

4. Interpretation

32All in all, the environmental evidence points to the ship tramping along rather locally, most likely collecting taxes from the rural population for a feudal, royal, or ecclesiastical landlord – perhaps victualing for the nearby royal castle of Vordingborg – as opposed to a ship involved in the export of what must be presumed to be processed and more effectively packaged agricultural products, for example from Zealand to the Hanseatic towns south of the Baltic, a trade that was quite substantial during the Middle Ages.

33A mundane vessel such as this does not appear to be the most likely place to expect (perceived) “foreign” building traditions to gain a foothold, serving as a reminder that shipbuilding was and is a lot more open to influence and technology transfer than perhaps often thought.


Warm thanks to the excavation and documentation team: Thomas N. Andersen, Andreas G. Binder, Andreas K. Bloch, Sigurd A. B. Bohr, Matko Čvrljak, Daniel P. Dalicsek, Massimiliano Ditta, Frederik D. Hyttel, Morten Johansen, Marie E. Jonsson, Tine V. Karlsen, Werner Karrasch, Nilas H. Møller, Tom Nicolajsen & Ines Šelendić, as well as a range of experts each contributing their particular area of expertise, often well beyond their contractual obligation: Claudia Baittinger, Mads C. Christensen, Peter S. Henriksen, Martin N. Mortensen, Morten Fischer Mortensen, Thora G. Nyborg, Anette H. Petersen & Kristiane Strætkvern (National Museum of Denmark), Aoife Daly (, Jesper Petersen (Natural History Museum of Denmark). The survey, excavation, and essential post-processing are financed by the Danish Road Directorate (Vejdirektoratet).

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Baittinger C.
2018 Vedanatomisk analyse af træliste fra Kalverev Syd VIR2794, Brede, NNU report 24/2018.

Bill J.
1995 “Getting into business. Reflections of a market economy in medie­val Scandinavian shipbuilding,” in O. Olsen, J. Skamby Madsen, F. Rieck (eds), Shipshape. Essays for Ole Crumlin-Pedersen, Roskilde, Viking Ship Museum, p. 195–202.

Daly A.
2015 “Dendrochronological analysis of medieval cargo ships from Danish waters,” in A. Englert, Large Cargo Ships from Danish Waters, 1000–1250, Roskilde, Viking Ship Museum, Ships and Boats of the North 7, p. 356–374.

Daly A.
2017 Dendrochronological analysis of timbers from a boat found at Kalve Rev, Denmark, København, report 35/2017.

Henriksen P. S., Mortensen M. F., Mortensen M. N. Christensen M. C., Taube M.
2018 Makrofossil- pollen- og tjæreundersøgelser af prøver fra Kalverev Syd-vraget, Brede, NNU report 17/2018.

Hocker F., Daly A.
2006 “Early cogs, Jutland boatbuilders, and the connection between East and West before AD 1250,” in L. Blue, F. Hocker, A. Englert (eds), Connected by the Sea, Proceedings of the Tenth International Symposium on Boat and Ship Archaeology (ISBSA 10), Roskilde 2003, Oxford, Oxbow books, p. 187–194.

Petersen A. H.
2018 Undersøgelse af kalfatringerne fra Kalverev Syd vraget VIR 2794, Brede, NNU report.

Petersen J.
2018a Insektanalyse af Kaverev Syd skibsvraget (VIR 2794), ArchaeoScience vol. XXI, Copenhagen, report.

Petersen J.
2018b Insects from tar patches in a medieval shipwreck from Kalverev Syd, Denmark, Quaternary Entomology Dispatch, p. 3–4.

Porsmose E.
1988 “Middelalder o. 1000–1536,” in C. Bjørn, T. Dahlerup, S.P. Jensen, E. H. Pedersen (eds), Det danske landbrugs historie I. Oldtid og middelalder, Odense, Landbohistorisk Selskab, p. 205–417.

Thomsen M.H.
2017 Kalverev Syd. Beretning for udgravning af middelalderlig vragdel, Roskilde, excavation report.

Vlierman K.
1996 … Van Zintelen, van Zintelroeden ende Mossen…. Een breeuwmethode als hulpmiddel bij het dateren van scheepswrakken uit de Hanzetijd, Lelystad, Ministerie van Verkeer en Waterstaat, Lelystad, Nederlands Institut voor Scheeps- en onderwater­Archeologie, Scheepsarcheologie I, Flevobericht 386.

Åkerlund H.
1951 Fartygsfynden i den forna hamnen i Kalmar: Kulturhistoriska undersökningar vid Kalmar slott utförda under ledning av Martin Olsson, Uppsala, Almqvist & Wiksells boktr.

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1  The site history and methodology is described in a forthcoming publication by Matko Čvrljak and the author.

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Table des illustrations

Titre Fig. 1: Location of the wreck site in the Storstrømmen sound
Crédits (drawing M. Thomsen)
Fichier image/jpeg, 631k
Titre Fig. 2: Site plan: photogrammetry overlaid with traced timbers and frame stations
Crédits (photogrammetry M. Čvrljak, drawing M. Thomsen)
Fichier image/jpeg, 3,3M
Titre Fig. 3: Distribution of botanical macrofossils
Crédits (drawing M. Thomsen after data from Henriksen et al. 2018)
Fichier image/jpeg, 718k
Titre Fig. 4: Distribution of insects by habitat
Crédits (drawing M. Thomsen after data from Petersen, J. 2018a)
Fichier image/jpeg, 835k
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Mikkel H. Thomsen, « The medieval shipwreck from Kalverev Syd, Denmark »Archaeonautica, 21 | 2021, 187-192.

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Mikkel H. Thomsen, « The medieval shipwreck from Kalverev Syd, Denmark »Archaeonautica [En ligne], 21 | 2021, mis en ligne le 01 juillet 2022, consulté le 05 décembre 2023. URL : ; DOI :

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Mikkel H. Thomsen

Viking Ship Museum in Roskilde

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