The construction of Staverns Fort began in 1677 when Ulrik Frederick Gyldenløve built a blockhouse with battery and palisades on a hill as part of the overall development of Norwegian fortresses. The fort was first built on Karlsøy during the Gyldenløve War (1675–1679). Fredriksvern and Fredriksvern Verft was established as the headquarters for the Norwegian Fleet from 1750 until 1758 so that the older fortification became part of the naval base and called the Citadellet and the island Citadelløya.
The fortress was expanded in 1687 until 1689 to include three canon batteries and a blockhouse. The fortress served as an important base for Norwegian naval hero Tordenskiold and his fleet during the Great Northern War’s final Norwegian phase from 1709 until 1720 and as a central staging point for sea commerce from Denmark in this period. The fort was the home port for the Danish–Norwegian Kattegat squadron. And not least, it served as a major chandelling and forwarding center for canon from the Norwegian ironworks and other equipment.
In the 1800s, Fredriksvern lost its importance as a military base. The Citadellet also lost its military importance and went into decline. In the 1900s, the buildings were restored. Krutttårnet, the oldest constructed building, has a distinctive architecture and today is a well known tourist attraction.
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.