In the 12th and 13th century, Näs (or Visingö) Castle on the southern end of Visingsö was the residence for the fragile Swedish monarchy. It was built probably by Sverker I of Sweden (died in 1156) or his son Charles VII of Sweden (Karl Sverkersson). Näs was thereby the oldest Royal castle in Sweden. It was a residence 5-6 kings before in 1318 Birger I (Birger Magnusson) pawned it to Danish. The castle was probably demolished soon after.
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.