St. Hallvard's Cathedral (Hallvardskatedralen), the former Oslo Cathedral, was the earliest cathedral in Oslo. The cathedral was built at the height of the Old Town market square Oslo during the early 12th century, and was used as a church until about 1655. Besides being the bishop's seat and religious center of eastern Norway for about 500 years, the cathedral was the coronation church, royal wedding church, chapel royal, and one of Scandinavia's most visited place of pilgrimage. St. Hallvard cemetery is located mainly south of the cathedral. It was the honorary cemetery in Oslo and eastern Norway from around 1130 to 1639. Here the bishops, chiefs and other prominent men and women were buried. The most prominent was interred in the church along with the kings.
Today the cathedral is in ruins. The main body in the ruins park (Memorial Park), the southern part under a concrete cap - and the concrete lid of the street of Bispegata. Towards the end of the 19th century were Bispegata extended in an easterly direction, over the cathedral site. It has been put in place to remove Bispegata's eastern part, as a result of the completion of the Ekeberg Tunnel and the modified veian resort in the lower Lodalen. In that case, the ruins of St. Hallvard Cemetery exposed, and the Medieval city triangular marketplace, Oslo squares, re-established west of St. Hallvard Cemetery. Neighboring the Cathedral was the smaller Church of the Cross.
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.