The Hohensyburg, a castle complex of the Lords of Sieberg, was constructed on the grounds of a former Saxon refuge, which was conquered in 775 by the Franks under Charlemagne. The castle, which was built around 1100 of Ruhr sandstone, was partially destroyed in 1287 by Count Eberhard I. von der Mark. The castle complex was an imperial fief of the von der Mark counts from 1300. This fiefdom was transferred to Brandenburg in 1609, and later to Prussia.
Two keeps, residential quarters (two-chamber system), the wall ring and the walls around the courtyard complex are still recognisable. In the inside of the castle is a war memorial by Fritz Bagdons.
References:Rosenborg Palace was built in the period 1606-34 as Christian IV’s summerhouse just outside the ramparts of Copenhagen. Christian IV was very fond of the palace and often stayed at the castle when he resided in Copenhagen, and it was here that he died in 1648. After his death, the palace passed to his son King Frederik III, who together with his queen, Sophie Amalie, carried out several types of modernisation.
The last king who used the place as a residence was Frederik IV, and around 1720, Rosenborg was abandoned in favor of Frederiksborg Palace.Through the 1700s, considerable art treasures were collected at Rosenborg Castle, among other things items from the estates of deceased royalty and from Christiansborg after the fire there in 1794.
Soon the idea of a museum arose, and that was realised in 1833, which is The Royal Danish Collection’s official year of establishment.