Modern historians suppose that the wealth of the Bjarmians was due to their profitable trade along the Northern Dvina, the Kama River and the Volga to Bolghar and other trading settlements in the south. Along this route, silver coins and other merchandise were exchanged for pelts and walrus tusks brought by the Bjarmians. In fact, burial sites in modern Perm Krai are the richest source of Sasanian and Sogdian silverware from Iran. Further north, the Bjarmians traded with the Sami. It seems that the Scandinavians made some use of the Dvina trade route, in addition to the Volga trade route and Dnieper trade route. In 1217, two Norwegian traders arrived in Bjarmaland to buy pelts; one of the traders continued further south to pass to Russia in order to arrive in the Holy Land, where he intended to take part in the Crusades. The second trader who remained was killed by the Bjarmians. This caused Norwegian officials to undertake a campaign of retribution into Bjarmaland which they pillaged in 1222. The 13th century seems to have seen the decline of the Bjarmians, who became tributaries of the Novgorod Republic. While many Slavs fled the Mongol invasion northward, to Beloozero and Bjarmaland, the displaced Bjarmians sought refuge in Norway, where they were given land around the Malangen fjord by Haakon IV of Norway in 1240. More important for the decline was probably that, with the onset of the Crusades, the trade routes had found a more westerly orientation or shifted considerably to the south. When the Novgorodians founded Velikiy Ustiug, in the beginning of the 13th century, the Bjarmians had a serious competitor for the trade. More and more Pomors arrived in the area during the 14th and 15th centuries, which led to the final subjugation and assimilation of the Bjarmians by the Slavs. The collaborationist Quisling regime planned to build Norwegian colonies in Northern Russia, following a future success of Operation Barbarossa, and which were to be named "Bjarmaland"; but these plans never came to be.