Homburg was first mentioned in documents in 1276. Gottfried I of Sayn from the House of Sponheim (1247-1283/84) transferred his castrum Homburg to the German King Rudolf of Habsburg, in order to place it under his protection. He received the castle back as an inheritance. The castle was the residence of the Counts of Homburg, an imperial fiefdom (Reichsherrschaft).
From 1635 Count Ernst von Sayn-Wittgenstein altered the castle to its present-day appearance. One hundred years later the line of Sayn-Wittgenstein-Berleburg took over its management; the structure then fell into disrepair. Not until 1904 was its decline halted and, in 1926, a museum, founded by Hermann Conrad, took over the premises. Today it is the Museum of Oberbergisches Kreis.
In 1999 during an excavation, a stone keep of about 12.5 metres diameter was uncovered. Experts estimate that it dates to the 11th century. A consequence of this was that the history of the castle had to be reassessed to that time.
At the beginning of 2005 the district council decided to upgrade the castle. Their plans included inter alia the expansion of the 'Red House' (Rotes Haus) and the construction of a central cash desk and toilet area. The old orangery was to be torn down and replaced by a new two-storey administration and exhibition building.
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.