Medieval border of German Empire between Lower Carniola (Kranjska) and Slavonia is the result of a lengthy process between the second half of the 10th and 13th centuries. By colonising the border forest and the Gorjanci-Žumberk hills the imperial border shifted from the approximate line along the Krka river over twenty kilometers to the southeast. The annexation of the new territory had been carried out mainly by the Carinthian dukes of Spanheim, the counts of Weichselburg and by the bishops of Freising and countsof Bogen with their ministerials. The new borderline was from the 13th century onwards defined by the castles and estates Gračeno, Žumberk (Sicherberg), Sicherstein, Vivodina (Herzogtum) and Metlika (Mötling). This border remained fixed until the 16th century when the Turkish raids caused an economic collapse and considerable ethnic changes. A wide border zone, settled by the refugees from the Balkans (Uskoki), became part of the Military Frontier (Vojna krajina). In the 18th century the border of Carniola was shifted back to the ridge of Gorjanci where from the dissolution of Vojna krajina (1881) up to the present day it has formed the new border with Croatia.