Larger cities usually retained their self-administration according to traditional German town law and formed exempt urban districts (Stadtkreise) comparable to independent cities. Often these cities also served as the administrative seat responsible for the smaller towns and villages incorporated into the surrounding rural districts, which then were called (Landkreise) for the purpose of differentiation (e.g. Stadtkreis and Landkreis Königsberg). The number of urban districts increased in the course of the Industrial Revolution and the following urbanization from the 1830s onwards.