Lilleborg is a ruined castle in the Almindingen forest. The castle was probably built in the middle of the 12th century as a royal fortress. It appears to have replaced the much larger fortress of Gamleborg which was only 700 metres away. The move could be explained by the fact that in 1149, three-fourths of Bornholm had been surrendered to Eskil, archbishop of Lund. As a result, King Sweyn III wanted to establish his own seat of power on the remaining fourth of the island. While it could not be compared to the archbishop's Hammershus, Lilleborg was nevertheless a fine stronghold and appears to have been easier to defend than the much larger Gamleborg. There is evidence suggesting the fortress burnt down in 1259 when Prince Jaromar of Rügen stormed and destroyed the 'king's stronghold' on Bornholm. However, coins minted after that date have been found, indicating it was inhabited after its storming.
Lilleborg's construction inland rather than on the coast has been compared to that of Refshaleborg on Borgø in Maribo lake. It had a large tower, 9.5 metres square, protecting the entrance to the courtyard. Its walls were 2.4 metres thick and from the top it was easy to hit anyone trying to attack. The fortress is further protected by a curtain wall which follows the cliff tops around the oval plateau. The interior was some 76 metres long and 41 metres wide. When its defenses were obsolete, the fort's stones were re-purposed for other buildings. From 2006 to 2011, restoration work was carried out at Lilleborg.
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.