Approximately 30km away from Sweden's capital Stockholm, in lake Mälaren, lies Björkö - a small island with great history. For Björkö is covered in Viking Age burials1 , some visible as grave mounds, others hidden beneath the soil. At the western border of the then-shoreline (which changed due to Scandinavia's post-glacial land rebounce) lies a former fortification surrounded by a rampart ("Borg"). North of this fortification is an area which, because of the dark colour of the soil, got the name "Svarta Jorden" - "the Black Earth"2 . Beneath this area rests a Viking Age town. Probably the first town to be founded in Sweden: Birka.

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Archaeological investigations and publications

The first archaeological investigations at Birka of greater scale were done in the 1870s under Hjalmar Stolpe2 . At first Stolpe traveled to the island out of entomological interest. He hoped to find insects enclosed in some of the amber stones which could be found there. But then he got curious about some old items lying on the ground. That there are cultural remains of archaeological interest on the island was already well known. But it were the excavations led by Stolpe that would unearth a substantial part of those remains for the first time after more than a thousand years.

The finds were described in more detail and catalogued in the first half of the 20th century; during the course of that century numerous studies were then published. The probably best known publications are the ones of the series "Birka I-V"(2 -10 ). Over the years more excavations took place, among these a bigger project with the focus on the "Black Earth" in the 1990s2 and two smaller projects in 2013 and 2014. Apart from many publications published in different journals, the publication series "Birka studies" emerged. A comprehensive list of publications has been created by the Historical Museum in Stockholm.

The finds of Birka are like a never ending treasure chest where re-enactors as well as archaeologists always find something new. So it is from the grave finds from Birka that a lot about our knowledge about Viking Age clothing come from8 11 12 13 14 ; some details are still a cause for discussion among the scientists15 . But the reality is that we know astonishingly little about Birka since only a small percentage of the area has actually been investigated1 .

"Virtual excavations"

An international team made out of scientists from the Ludwig-Boltzmann Institute for archaeological prospection and virtual archaeology (LBI ArchPro) and the archaeologists of RAÄ started a project to change this lack of knowledge. By using so-called "archaeological prospection", almost the entire site has been mapped over the past years16 . The method, supported by modern technology, enables the scientists to "look into the ground" and search for structures of archaeological interest by e.g. measuring the magnetic resistance of the ground and the structures within (magnetometer) or by probing the ground with a radar (GPR = Ground Penetrating Radar). Unlike excavations, which are usually done in a much smaller scale, only give a tiny glimpse into a greater complex1 and often are of destructive nature, observations conducted with archaeological prospection help to bring hidden structures into a greater context in a non-invasive way.

First results - old and new town rampart

The first field work was done in 200617 18 . A restricted area on the Black Earth as well as a smaller area that should cover the assumed continuation of the so-called town-rampart at the border of the northern grave field "Hemlanden" were investigated using magnetometry and GPR.

Some archaeological prospection has already been conducted along the assumed continuation of the town rampart in the 1990s19 , but without any indication of clear archaeological structures18 . Some stones lying on the surface along the assumed continuation line could be interpreted as foundations. The magnetometry results showed more stones in the subsurface of the same line17 18 . Although there are several openings in the rampart which makes it practically useless as a defense1 , the continuation towards Borg appeared almost to be proven. After another mapping of that area with GPR in 201116 , however, no traces of a continuing rampart were visible; instead, the results showed a great amount of previously unknown graves1 . The stones interpreted as a foundation for a rampart proved to be features belonging to graves(Trinks 2017, pers. comm.).

During the analysis of the GPR data from the Black Earth area, the scientists made a surprising discovery18 : Birka's first town rampart17 18 . This structure is not visible from the outside anymore, possibly because of farming in the past. The eastern part is most likely made of clay and has a gate with a possible gatehouse, whereas the western part towards the shoreline was made of a different material, maybe of a wooden palisade with stone foundations17 . Towards the western end of the clay part a boat-shaped structure can be found. Whether this is a hidden grave of whether the rampart was fortified using old boats still needs to be evaluated.

Property boundaries, outlines of houses and alleyways are visible inside as well as outside the old rampart. Next to many smaller buildings there are traces of a bigger one (ca. 12x5m) with several post holes, a central hearth and and slightly outwards curving outlines. Property boundaries outside the rampart could be interpreted as farmsteads or animal pastures while inside there were workshops, stores and trading places of different kinds18 . Anomalies above the traces of the rampart could be interpreted as signs of Birka's expansion17 .

Large-scale mapping

In 2008, a bigger area was investigated which covered, among other things, that older town rampart, aiming for more detailed results20 . Using more up-to-date equipment than in the previous years, is became possible to plot even post holes with a diameter of only 25cm. Different phases of settlement construction became visible, complicating the archaeological interpretation to a degree. Outside the rampart, the archaeologists recognized trenches, wells, buildings and property boundaries which were easier to identify. Some of the trenches could even be the ones dug by Hjalmar Stolpe during his excavations in the Black Earth - their location has not been recorded so that it remained unknown until today which areas were disturbed by him.

In 2011 a total area of 59.8 hectare was mapped using magnetometry and GPR, eventually16 . Those areas with a rough topography and two fields with crops were excluded from the investigations. In December, the island was mapped using an airborne laser scanner in order to generate a digital terrain model without irritating vegetation onto which the geophysical data could be projected.

Apart from the rediscovery of Stolpes trenches from the 1870s the archaeologists were able to identify alleyways, buildings, fortifications and many grave mounds leveled out by ploughing as well as other grave types16 . It became obvious that the grave field Hemlanden continued towards "Borg"16 - and that the total number of graves on the island was, instead of about 2000, more likely to be about 4000-50001 .

In the former town area, the Black Earth, different phases could be identified which are marked by different sizes, types and arrangements of buildings1 21 . Also, north of and outside the town traces of a house built in the typical Nordic longhouse style were found (most of the houses inside the town were smaller and of a different shape)1 . This building was without any fortifications and could have played a special role in the context of Birka1 .

The results of this archaeological prospection not only help to interpret former finds in the greater context of the settlement. Most of all, they give the possibility to get insights into Birka's history like it was never possible before. During the investigations it became clear to the scientists that in the beginning, Birka was far from being the peaceful trading paradise which dominated the view of Sweden's first town for so long1 .


  1. vetenskapens värld säsong 26 avsnitt 8; 10.10.2016. (
  2. Ambrosiani, B. och Erikson, B. 1991. Birka Vikingastaden Vol. 1-Jakten på Svarta jordens hemligheter har börjat.
  3. Arbman, Holger. Birka: Untersuchungen und Studien. 1, Die Gräber: Tafeln. Vitterhets-, historie-och antikvitetsakad., 1940.
  4. Arbman, Holger. Birka: Untersuchungen und Studien. 1, Die Gräber: Tafeln. Vitterhets-, historie-och antikvitetsakad., 1940.
  5. Arwidsson, Greta. "Birka II: 1: systematische Analysen der Gräberfunde." Stockholm: Royal Swedish Academy of Letters (1984).
  6. Arwidsson, Greta. Birka II: 2: systematische Analysen der Gräberfunde." Stockholm: Royal Swedish Academy of Letters (1986)
  7. Arwidsson, Greta. Birka II: 2: systematische Analysen der Gräberfunde." Stockholm: Royal Swedish Academy of Letters (1989)
  8. Geijer, Agnes. "Birka III." Die Textilfunde aus den Gräbern (1938).
  9. Gräslund, A. S. "Birka IV." The burial customs. A study of the graves on Björkö (1980).
  10. Duczko, W. "Birka V." The filigree and granulation work of the viking period–An analysis of the material from Björkö (1985).
  11. Hägg, Inga. Kvinnodräkten i Birka. Vol. 2. Institutionen för arkeologi Gustavianum [Uppsala universitet], 1974.
  12. Hägg, I. "Birkas orientaliska praktplagg. Fornvännen 78: 3–4." Journal of Swedish Antiquarian Research (1983): 204-223.
  13. Hägg, Inga. "Die Tracht." Birka II 2 (1986): 51-72.
  14. Hägg, Inga. "Vikingatidens Kvinnodräkt." Historiska nyheter 61 (1990).
  15. Hägg, Inga. "Textilien und Tracht in Haithabu und Schleswig. Die Ausgrabungen in Haithabu 18" Wachholtz Verlag/Murmann Publishers (2015)
  16. Trinks, Immo, et al. Archaeological Prospection of the UNESCO World Cultural Heritage site Birka–Hovgården. na, 2013.
  17. Trinks, I., and L. I. Larsson. "Undersökning utan utgrävning. Kartläggning av Birka. Geofysiska prospekteringsmetoder I. Arkeologiska undersökningar har givit ny kunskap om vikingastaden Birkas uppbggnad och utveckling." Populär Arkeologi 3 (2007).
  18. Trinks, Immo, Wolfgang Neubauer, and Alois Hinterleitner. "First High‐resolution GPR and Magnetic Archaeological Prospection at the Viking Age Settlement of Birka in Sweden." Archaeological Prospection 21.3 (2014): 185-199.
  19. Wåhlander, L. "Birkas stadsvall och dess förlängning fram till Borg." CD-uppsatser i laborativ arkeologi 97 (1998): 98.
  20. Trinks, Immo, et al. "Efficient, large‐scale archaeological prospection using a true three‐dimensional ground‐penetrating Radar Array system." Archaeological Prospection 17.3 (2010): 175-186.
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