Bishop Arnaldur (1124-52) returned to Norway in 1150 from Gardar, Greenland and was appointed first Bishop of Hamar. He began to build the cathedral, which was completed about the time of Bishop Paul (1232-52). Bishop Thorfinn of Hamar (1278-82) was exiled and died at Ter Doest in Flanders. Thorfinn and many other bishops of the area disagreed with the sitting King Eric II of Norway regarding a number of issues, including episcopal elections. Bishop Jörund (1285-86) was transferred to Trondhjem.
In the aftermath of the Reformation in Norway, the structure was renamed Hamarhus fortress and made into the residence of the sheriff. The cathedral was still used but fell into disrepair culminating with the Swedish army’s siege and attempted demolition in 1567, during the Northern Seven Years' War. Swedish forces had launched attacks into Eastern Norway, capturing Hamar and continued towards Oslo. The Swedes later retreated, torching Hamar on their way, destroying Hamar Cathedral and Hamarhus.
Today the ruins of Hamar Cathedral form a part of the Hedmark museum (Hedmarksmuseet). The ruins of what remain of the Hamar cathedral, were originally built in Romanesque architecture and later converted to Gothic architecture. The distinctive arches in the cathedral ruins are covered in one of the most ambitious construction projects of its kind undertaken by the Norwegian government.
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.