Gråborg is the largest ancient castle in Öland. It was built probably in the 6th century and enlarged through Middle Ages. According old tax reports dating back to the year 1450, Gråborg was owned by Vadstena abbey and functioned as a some kind of trade center. It was used for defence against Danish even in 1677. According to legend Gråborg was strongly associated with king Burislev Sverkersson who had grown up there with his half-sister Sofia of Minsk.
Gråborg Castle consisted of a circular wall, about 4-7 meter tall. There were three entrances and one of them was vaulted in the Middle Ages. Archaeological excavations have revealed lot of findings, which are stored today in Kalmar Museum.
There are medieval ruins of the chapel of St. Knut on the north side of castle.
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.