Otto I laid the basis of the organization of the Church in this territory by making the chief fortified places which he established in the different marks the sees of dioceses. In 960 Otto I had transferred the ducal authority over Saxony to Margrave Hermann Billung, who had distinguished himself in the struggle with the Slavs, and the ducal title became hereditary in Count Hermann's family. This old Duchy of Saxony, as it is called in distinction from the Duchy of Saxe-Wittenberg, became the centre of the opposition of the German princes to the imperial power during the era of the Franconian or Salian emperors.