 One of his most impressive works is "Freiheit der teutschen Kirchen", where he describes the constant struggle between the Roman-German emperors and the popes since the Pope Gregory VII.in the 11th century.In contrast to the popes the Roman-German emperors had no absolute power and the highest authority in the Holy Roman Empire was not the emperor, the Kaiser, but the "Reichsversammlung" (Imperial Assembly), especially its most prominent members, the "Kurfürsten" (Electors) whose task was to elect the Kaiser.