<p>Abstract: Previous research on the Viking Age trade centre of Birka has suggested the parallel use of two harmonising standard weight units, differing in mass by five percent. As an explanation to this phenomenon, this paper puts forward a hypothesis of a trading fee, embedded in the weights. This is corroborated through a hypothetical deductive study; including a reassertion of earlier results by means of a new method for archaeometrological analysis, using a 3D scanner and Computer-Aided Design. Further, the role of silver, as a preferred unit of payment in Birka, is supported through a spatial analysis of the distribution of Islamic coins and Oriental beads in the provinces of Middle Sweden. Plausible manufacturing sites for the cylindrical lead weights, adhering to the Birka mitqal, are discussed as a possible way of falsifying the hypothesis. The results suggest that a trading fee was extracted, using the Birka mitqal for imports and the Islamic mitqal for exports. The metrological analysis was also expanded to weights from Sigtuna, which proved the Birka mitqal, as well the dual metrics system, continued to be in use there until, at least, the first half of the 11^th century. Finally, a short study on the origins of the Scandinavian/Islamic weight system suggests that the direct influence for the system primarily can be attributed the Volga-Bulgarians.</p>

Abstract: Previous research on the Viking Age trade centre of Birka has suggested the parallel use of two harmonising standard weight units, differing in mass by five percent. As an explanation to this phenomenon, this paper puts forward a hypothesis of a trading fee, embedded in the weights. This is corroborated through a hypothetical deductive study; including a reassertion of earlier results by means of a new method for archaeometrological analysis, using a 3D scanner and Computer-Aided Design. Further, the role of silver, as a preferred unit of payment in Birka, is supported through a spatial analysis of the distribution of Islamic coins and Oriental beads in the provinces of Middle Sweden. Plausible manufacturing sites for the cylindrical lead weights, adhering to the Birka mitqal, are discussed as a possible way of falsifying the hypothesis. The results suggest that a trading fee was extracted, using the Birka mitqal for imports and the Islamic mitqal for exports. The metrological analysis was also expanded to weights from Sigtuna, which proved the Birka mitqal, as well the dual metrics system, continued to be in use there until, at least, the first half of the 11th century. Finally, a short study on the origins of the Scandinavian/Islamic weight system suggests that the direct influence for the system primarily can be attributed the Volga-Bulgarians.