Dalmatian cities retained their culture and language for a long time. Dalmatian Romance was spoken until the high Middle Ages, but, they too were eventually assimilated into the body of Slavs. In the Western Balkans, South Slavs and Germanic Gepids intermarried with invaders, eventually producing a Slavicized population. In Central Europe, the West Slavs intermixed with Germanic, Hungarian, and Celtic peoples, while in Eastern Europe the East Slavs had encountered Finnic and Scandinavian peoples. Scandinavians (Varangians) and Finnic peoples were involved in the early formation of the Rus' state but were completely Slavicized after a century. Some Finnic tribes in the north were also absorbed into the expanding Rus population. In the 11th and 12th centuries, constant incursions by nomadic Turkic tribes, such as the Kipchak and the Pecheneg, caused a massive migration of East Slavic populations to the safer, heavily forested regions of the north. In the Middle Ages, groups of Saxon ore miners settled in medieval Bosnia, Serbia and Bulgaria, where they were Slavicized. Saqaliba refers to the Slavic mercenaries and slaves in the medieval Arab world in North Africa, Sicily and Al-Andalus. Saqaliba served as caliph's guards. In the 12th century, Slavic piracy in the Baltics increased. The Wendish Crusade was started against the Polabian Slavs in 1147, as a part of the Northern Crusades. The pagan chief of the Slavic Obodrite tribes, Niklot, began his open resistance when Lothar III, Holy Roman Emperor, invaded Slavic lands. In August 1160 Niklot was killed, and German colonization (Ostsiedlung) of the Elbe-Oder region began. In Hanoverian Wendland, Mecklenburg-Vorpommern and Lusatia, invaders started germanization. Early forms of germanization were described by German monks: Helmold in the manuscript Chronicon Slavorum and Adam of Bremen in Gesta Hammaburgensis ecclesiae pontificum. The Polabian language survived until the beginning of the 19th century in what is now the German state of Lower Saxony. In Eastern Germany, around 20% of Germans have historic Slavic paternal ancestry, as revealed in Y-DNA testing. Similarly, in Germany, around 20% of the foreign surnames are of Slavic origin. Cossacks, although Slavic and practicing Orthodox Christianity, came from a mix of ethnic backgrounds, including Tatars and other peoples. Initially, the Cossacks were a mini-subethnos, but now they are less than 5%, and most of them live in the south of Russia. The Gorals of southern Poland and northern Slovakia are partially descended from Romance-speaking Vlachs, who migrated into the region