The basis of the present-day linguistic structure was provided by settlement in the area. In the case of the old-established territories west of the rivers Elbe and Ohre, this came during the migrationary period of the Germanic peoples, while in the neighbouring Altmark it was later and dates from the ninth century. The originally Slavonic territories to the east of the Elbe and Saale rivers were settled later, in the twelfth century, by Germans from west of the Elbe and Ohre. The settlers in each instance brought with them different Low German dialects. Large-scale linguistic levelling took place within the feudal territories of the late Middle Ages (Duchies, etc.), the most extensive and politically influential of these territories being Mecklenburg, West Pomerania ( Vorpommern), Brandenburg with the Altmark (later Prussia) and the region around Magdeburg with the area east of the Elbe around Genthin (belonging to Brandenburg from the seventeenth century) which remained in essence unaltered as a core up to the nineteenth and twentieth centuries. Over the centuries the former Anhalt Duchy of Zerbst had stronger connections with Brandenburg, while the area around Wittenberg always belonged to southern political territories.