Tinnumburg is the best preserved of the three ancient ring forts in Sylt. The fort was built around the birth of Christ. The rampart has a diameter of 120 meters. The wall is up to seven meters high and has a circumference of about 440 meters. The castle had at least two gates (east and south).
Excavations in 1870, 1948 and 1976 provided evidence that the Tinnumburg was built in the style of early Roman Empire round ramparts on the North Frisian islands. The excavations have shown that this is a Germanic site of worship. The fort was in use again in the 8th to 10th centuries.
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.