348 Rus principalities (1050s–1238) Mongol armies under Batu Khan brought the period to its end with the destruction of Kiev, Riazan, Vladimir, and many other towns from 1237 to1239 FOUNDATION PERIOD The main written account for the foundation period is the Russian Primary Chronicle, compiled by monks at the Kievan Caves Monastery in the early 12th century Archaeological and numismatic evidence serves as a supplement and corrective to this problematic account These sources trace the early formation of the Rus lands to the Volkhov-Il’men river basin of northwestern Russia Finno-Baltic hunter-gatherers inhabited this densely forested marshy region In the mid-eighth century Slavic agriculturalists began migrating to the area from the south At the same time Scandinavians began small-scale raiding/trading expeditions to the region The convergence of these groups served as the initial catalyst for the development of a new politicalcommercial community Forces at play in both northwestern Europe and the Middle East explain Scandinavian movement into Russia Lacking locally exploitable sources of silver, which was needed for northwestern European political and commercial expansion, the early medieval kingdoms of the Anglo-Saxons and Franks looked to the Near and Middle East, where, from the mid-eighth century, the Abbasid Caliphate centered in Baghdad minted millions of silver coins (dirhams) annually The Vikings acted as the middlemen for this trade Beginning sometime in the mid- to late-eighth century, small groups of Vikings set up way stations in the Volkhov-Il’men and Upper Volga basins They collected furs from the FinnoBalts and Slavs in northwestern Russia and sailed south to trading ports on the Volga River and Caspian Sea, where they would exchange furs, Frankish swords, and walrus ivory for eastern luxury items, especially silver Yaroslav the Wise sponsored major building campaigns in Kiev, which imitated the architecture of Constantinople He imported Byzantine master builders to construct the Church of St Sophia (which was also decorated by Byzantine mosaicists)