Soon after the Erkelenz was elevated to a town status in the 12th century, work began on the brick fortifications of the place. These probably consisted of basic ramparts as had been common since time immemorial for the defence of settlements. Although the castle was not documented until 1349, the town appeared to have developed under the protection of the castle.
The castle has 23 high keep, curtain walls and corner towers. It was part of larger city walls. It was badly damaged by French army in 1674.
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.