The lands of Rostov-Suzdal Principality were settled by Slavs in this period, with the native Finno-Permic speakers being gradually assimilated. In the North the territories between Onega and Ladoga lakes and along Svir, Northern Dvina and Vyatka rivers attracted Novgorodian settlers. The Mongol invasion triggered an internal migration from less secure Southern lands to the forested regions of Moscow, Tver and Upper Volga.