In 1299, Haakon V Magnusson was proclaimed king of Norway. As a duke, his administration had previously been bases in Oslo, which obtained ist status as the captial of Norway during this period. The King initiated the construction of the fortress some time before the turn of the century. The medieval castle, which was completed in the 1300s, was strategically placed at the very end of the headland. Thus, it withstood a number of sieges throughout the ages. King Christian IV (1588-1648) had the castle modernized and converted into a Renaissance castle and royal residence. In the 1570s, the castle became the residence of the Danish King Governor of Norway. During the 17th and 18th century the castle fell into decay, but restoration work started in 1899.
The prison Museum
As early as 1830 50-60 prisoners were imprisoned here. In 1853 the tower got one extra floor, whitch contained 8 new cells. In the 1890s three punishment cells were built on the ground floor. It was here the masterthief Ole Høiland was imprisoned - and escaped from. During the Second World War the tower was used to imprison Norwegian patriots who waited to be executed.
The Armed Forces Museum
The two brick buildings at the far end of the fortress yard were built in the 1860s and used as arsenals. They provide as natural setting for the museum, which was opened in 1978. The Armed Forces Museum is a historical museum, depicting Norwegian military history, from the very first defence measures taken during the Viking era, through the numerous Nordic wars under Danish rule, the period leading up to independence (1814-1905), as well as modern history, including the Second World War.