Akershus Fortress is an important part of the City of Oslo's identify. The core of what is now the centre of the capital city (the Kvadraturen area) was established outside the walls of Akershus Fortress in 1624. The fortress is a national symbol because of its role as a royal seat of centre of state power, and because of the many important and dramatic historical events that have taken place there. Its national importance is underlined by the fact that, even today, it is the Norwegian Government's principal venue for official functions and state occasions. It also houses the Royal Mausoleum.
Akershus Fortress consists of two parts – the inner and outer fortress.
Akershus Castle is the most important building in the inner fortress. The buildings here date back to the Middle Ages, but were developed in many different stages before the whole site was restored in the 20th century. Here, visitors can see both the medieval fortress and the Renaissance castle, which is representative of 17th century architecture.
In the inner fortress area, there are also several buildings dating from the 17th to the 19th centuries, including several buildings that were originally used as depot buildings, but that have been converted and now house an educational centre, as well as buildings that originally served as a prison and prison church. The inner fortress is surrounded by a bastion fortress with outworks, which was mostly planned by Steenwinckel and on which building work started in 1592.
The fortifications were completed in the mid 1600s under the leadership of fortifications engineer Isaac van Geelkerck. Substantial fortifications were also built outside the bastion, but most of them were demolished from the early 19th century and during the next hundred years.
In the outer fortress there are fortifications and buildings from the second half of the 18th century and the 19th century. There is a drill ground, school buildings, the Commandant's Quarters and arsenal buildings. Today, the buildings also house government offices and the Norwegian Armed Forces Museum.