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Birka’s Harbour in Excavation and Surveys

Dr. Sven Kalmring

Feodor Lynen Research Scholarship of the Humboldt-Foundation

Located on an island in the Lake Mälar region, Birka, like Haithabu, is one of the few large proto-urban centres and nodal points in the long-distance trade network of the Viking Age. Both places are similar not only in size and various structural details as e.g. the fortifications but also in their similarities which are passed down in historical sources regarding missions and establishment of church by St Anskar, the administration of the vici by a representative installed by the king. Various scholars have pointed out several connections between the two maritime trading sites from an early stage, such as Swedish archaeologist Sune Lindqvist in his article “Hedeby och Birka” published in 1926 in “Fornvännen”. The study of the Viking Age harbour of Haithabu which is presented in the context of a PhD thesis forms an important starting point for the investigations of the harbour of Birka.

Birka Harbour Excavation
The trading place of Birka (8th century to last quarter 10th century) is located on the island Björkö, c. 30 km west of Stockholm. Other than today the Lake Mälar region was at the time of the Viking Age an extended Baltic bay. Only in the 10th century was it separated from the Baltic Sea due to post-glacial land uplift. Situated at the nodal point of the two most important sailing routes in central Sweden, this early town was at a strategically very advantageous location. For one it was the crossing point of the East-West running transport axis, from the interior to the Baltic Sea. On this route Birka was an important location for transshipping and stacking of trading goods like iron or wood which were transported in winter on sleds overland from central Sweden. The second transport axis was the so-called Fyrisleden. It led from the Baltic in the south across the sound at Södertälje into Lake Mälar and past Birka towards Sigtuna, Gamla Uppsala and Vendel in the north of the Mälar valley.
Today, Birka’s harbour is largely landfast due to the ongoing regression and sinking sea level.

Book cover Birka

However, a jetty has been documented by the excavations of B. Ambrosiani and B. Arrhenius in 1969–1971. Aim of the excavation in the settlement area Svarta jorden (“black earth”) was to identify the Viking-Age coastal line and to investigate the potential harbour area. One of two stone pavements has been excavated and proven to be a two-layer foundation of a jetty. It had been built at the humid coast environment and near a sand bank which had formed around a shoreline stabilisation built out of round timber. Its purpose was probably to fortify the wooden jetty.
The stratified finds from the excavation allow dating the stratigraphic sequence to the mid-ninth century up to the final stage of Birka around 970 AD. The jetty (“latest jetty”) dates to 930–950 AD.
Traces of an older similarly constructed jetty have been found below the tenth-century one, embedded into a 9th-century layer (“lower jetty”).
In 1990–1995 an excavation was carried out above the excavation site from 1969–1971 during which a layer of up to 0.8 m large stones was discovered, pointing out of the eastern profile wall of the 1990-trench. These stones were interpreted as being the front of another jetty (“earliest jetty”), located at c. 6.10-6.30 m above sea level.

3-D Model Birka
Kugghamn, Korshamn and Salviksgropen are under consideration as further inner harbours. Other stone foundations of two jetties are located off of the trading port below the garrison. It is assumed that a boat-house of the type naust can be found in the south of the island Björkö near Charlottenlund. Since 1970 dive campaigns are carried out regularly in the area in front of Svarta jorden in order to explore the part of the harbour that remained under water. Several drilling cores from the drillings from 1990/1991 provide information about the structure of the harbour sediment. Further important evidence comes from a yet unpublished geomagnetic survey in the landward part of the harbour, carried out in 2007.
The Feodor Lynen Research Scholarship for postdoctoral researchers at the Alexander von Humboldt Foundation, awarded on November 3rd 2010, enables a two-year stay since February 2011 at the Arkeologiska Forskningslaboratoriet of the University of Stockholm in order to conduct the research project “Birka’s Harbour in Excavations and Surveys” on site. The aim of the research project is to gather for the first time all information about Birka from excavations and surveys and interpret them against the background of conclusions from Haithabu as a whole. This will occur in close cooperation with the Swedish colleagues from the Arkeologiska forskningslaboratoriet (AFL), Statens Historiska museet (SHM), Riksantivarieämbetet (RAÄ), Sjöhistoriska museet and the Maritime Archaeological Research Institute (MARIS) at Söndertörns högskolan. The harbour is not only one specific aspect of the proto-urban centre Birka but being the economic core of the maritime trading site contributes crucial information for the understanding of the early town as a whole.

Birka’s Black Earth Harbour – Preparing the New Field Campaign


Dr. Sven Kalmring



In late summer 2014 a re-excavation of Birka’s Svarta jordens hamnområde from 1970/71 as well as an extension of the trial trench trough „the harbour’s waste zone“ from 1969 in front of the jetties was aspired. Aim was at one hand to get a better understanding of the wooden continuation of the so-far known stenkistor – wooden boxes filled with stones placed on the former shoreline –, on the other to make a connection to the ongoing underwater surveys from the Sjöhistoriska museet by expanding the old trial trench by another 13 meters (cf. Jahresbericht 2013). While the permission from Riksantikvarieämbetet was granted an authorization from Länsstyrelsen is still due. Currently the new field campaign is contemplated for 2015.

    In preparation of the upcoming field campaign a two-day geophysical survey in cooperation with Andreas Viberg from the Arkeologiska forskningslaboratoriet at Stockholms universitet was conducted in November 2014. By terms of a georadar survey in front of the stone boxes from 1970/71 down to the current shoreline with an extremely dense profile grid a total area of c. 20 x 40 meters could become covered. Aim was to record at least of one harbour facility in its total extent by means of post and postholes preserved in the “blue clay” (marine gyttja?) underneath the cultural layer strata. Contemporaneously the preparations within the Birka Town GIS were continued by the digitalisation of the (hitherto unpublished) excavation documentation from 1969 as well as the profile drawings from 1970/71 figured in the RAÄ-rapport “Svarta jordens hamnområde”. The documentation was transferred into a coherent 3D-model and now offers for the first time a unique overall view which will be particularly valuable for future surveys and analysis.


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Docent Dr. Sven Kalmring
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