On the metrology of Birka and early Sigtuna – tools of trade in the Viking Age Lake Mälaren Valley (Sweden)

Abstract

This paper analyses weights from the site of Birka, the main centre for trade in the Lake Mälaren Valley during the Viking Age, as well as its successor, the medieval town of Sigtuna, with the purpose of identifying which weight system was employed for trade in the area and period. The results show that the system was a local variant (the Baltic Sea system) of the contemporary weight system of the Caliphate. Further, the paper deals with the reasons for implementing this system and why it remained in use in Sigtuna even after trade had shifted to areas where other weight systems were decreed. We propose that the increased trade with Western Europe in the late 10th century to a large extent was conducted via the Western Slavonic region, which would, at this time, still have employed the Baltic Sea system, and further that direct trade with monetary economies such as the Holy Roman Empire and England would have given little incentive for change.