During the Early Middle Ages there was a small fort and church on the top of the Thun castle hill. The castle was built between 1180 and 1190 by Duke Berthold V of Zähringen, who constructed the still preserved keep to the level of the Knights' Hall (Rittersaal). The 14 m tall Knights' Hall was built as the centerpiece of a monument to Zähringen power. However, the family never lived in the castle, preferring Burgdorf Castle.
In 1218 it was inherited by the House of Kyburg, who built the upper levels above the Zähringen castle. A quarrel over who would rule the southern Kyburg lands led, in 1322, to Eberhard II von Kyburg murdering his brother Hartmann II at the castle. To protect his newly acquired land from the Habsburgs Eberhard II then sold them to Bern and was promptly given them back as a fief. The Kyburgs ruled over the region for nearly two centuries until a failed raid by Rudolf II on Solothurn, in 1382, started the Burgdorferkrieg. After several decisive Bernese victories the Kyburgs were forced to concede an unfavorable peace. In 1384 Bern bought Thun and Burgdorf, the most important cities of the Kyburg lands. The castle came under Bernese control and became the seat of their local administration.
The massive roof (1430–36) comes from the Bernese period. Due to the lack of residences in the castle, in 1429, an administrative and residential wing was added to the west of the keep, built in late Gothic style, and known as the 'new castle'. The castle was the seat of the local court and since at least the 17th century there was a prison under the roof of the donjon. In 1886 a new prison was built on the castle grounds. Two years later, in 1888, the museum opened in the castle. For a time the jailer was also the ticket seller and guard for the museum.
The castle museum is housed in the five floors of the tower, and includes cultural and historic displays showing the development of the region over some 4,000 years. It is open daily between February and October, and on Sundays only for the rest of the year. The great hall is used for concerts or plays, and can be hired for private events.
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.