The islet of Bornholm lies in the Baltic 47 km off the Swedish shore. There are ferries to Ronne on Bornholm from Copenhagen and from the German harbor of Sassnitz. The isle consists of a huge throng of granite, much of it with only a skinny layer of soil; on the north it is surrounded by gorgeous, steep cliffs and on the southeast and west by sand dunes; the area near Dueodde is mainly popular. The interior is festivity wooded and partially heath land. Until the 2nd century B.C., Bornholm was occupied by Burgundians (Burgundarholm). In the 12th C. the isle fell to the the Archbishopric of Lund (Hammershus Episcopal Castle). The Romanesque round churches, such as those at Osterlars and Olsker, were used as citadels in the war against the piratical Wends.