Already in the Middle Ages, various German dialects of the new-come settlers became widely used throughout Lower Silesia and some Upper Silesian cities. However, after the era of German colonization, the Polish language was still predominant in Upper Silesia and parts of Lower and Middle Silesia north of the Oder river. Germans usually dominated in large cities and Poles lived mostly in rural areas. This required the Prussian authorities to issue some official documents in Polish or both in German and Polish. The Polish speaking territories of Lower and Middle Silesia, commonly described until the end of the 19th century as the "Polish side" were mostly Germanized in the 18th and 19th centuries, except for some areas along the northeastern frontier.