Akershus fortress

Akershus slott og festning Castle and Fortress
Oslo, Norway
Akershus Castle and Fortress
Site information
Controlled by	Norway
Site history
Built	1290s
In use	1290s–present
Materials	Stone

Akershus Fortress (Norwegian: Akershus Festning) or Akershus Castle (Norwegian: Akershus slott) is a medieval castle that was built to protect Oslo, the capital of Norway. It has also been used as a prison.

It is not known exactly when the construction of the castle started but it is believed that it happened around the late 1290s, by King Haakon V, replacing Tønsberg as one of the two most important Norwegian castles of the period (the other being Båhus). It was constructed in response to the Norwegian nobleman, Earl Alv Erlingsson of Sarpsborg’s earlier attack on Oslo that occurred in 1287. In the aftermath of the attack, it became clear that the city’s existing defences weren’t effective and therefore, a stronger defensive centre was needed.

The castle is mentioned in written sources for the first time in 1300 in a letter from king Haakon to a church in Oslo. However, the letter does not mention how far the construction of the castle has progressed by then.

The fortress has successfully survived all sieges, primarily by Swedish forces, including those by forces led by Charles XII in 1716. In the early 17th century, the fortress was modernized and remodelled under the reign of the active King Christian IV, and got the appearance of a renaissance castle.

The fortress was first used in battle in 1308, when it was besieged by the Swedish duke Eric of Södermanland, whose brother won the Swedish throne in 1309. The siege was eventually broken by a local Norwegian army in a battle. (This battle forms a major part of the plot of Sigrid Undset historical novel "In the Wilderness", the third volume of her tetralogy The Master of Hestviken.)