Borgholm Castle is today only a ruin of the fortress that was first built in the second half of the 12th century and many times rebuilt in later centuries. The construction of the original fortress was probably ordered by king Canute I (1167-1195), who ordered fortresses to be built on the Swedish east coast as defence against enemies from the other side of the Baltic Sea. During the 13th to 15th centuries, additions and changes were made. New towers were built, a new and thicker wall was raised for example. The fortress was damaged on a number of times during these centuries, including in 1361, when king Valdemar IV (Atterdag) of Denmark attacked Borgholm.
During the Kalmar Union, many castles and fortresses in Sweden were damaged as a result of the ongoing conflicts between Danes and Swedes. John III (r. 1568-1592) ordered the reconstruction of Borgholm into a renaissance castle. During his reign, the Pahr brothers (four engineers and architects from Milan) led a significant rebuilding that took place from 1572. The castle acquired a Gothic character and became exemplary of the Italianate bastion style.
Some decades later, Sweden and Denmark fought each other in the Kalmar War. Borgholm Castle first, in 1611, surrendered to the Danish side, but was reconquered by the Swedish side later the same year. The following year, after a siege two weeks long, the commander of the Swedish defence, Peter Michelsen Hammarskiöld had to surrender. In accordance to the treaty that followed the war, the Treaty of Knäred, Borgholm was handed back to the Swedish.
The castle was in a bad shape after the war and it took until 1654 before a restoration and reconstruction would begin. This time, the castle was to be turned into a baroque palace. Charles X Gustav was the king that ordered this, and Nicodemus Tessin the Elder was the architect that was used to fulfil the king's wishes. When Charles Gustaf died in 1660, the construction stopped, only to be restarted at a slow pace during the following kings Charles XI and Charles XII. In 1709, the construction was ended totally and finally.
For a hundred years, the palace was left to fall into decay. On 14 October 1806, the castle was turned into a ruin through a fire that started in the roof of the north wing. The castle of today is the ruins of the 17th century baroque palace Charles X Gustav had constructed. It is owned and superintended by the National Property Board of Sweden. It is open for visitors and holds a museum.
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.