The Mandraki was the military harbour and was guarded by a tower built between 1464 and 1467 by the Grand Master Zacosta at the end of the natural mole. After the siege of Rhodes in 1480 the Grand Master d'Aubusson added a bastion around the tower transforming it into a guard fortress on the sea.
The castle was built at the place of an old Byzantine church dedicated to St. Nicholas, hence the name. Since the 17th century, a lighthouse was added at the top.
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.