Karlsborg Fortress is one of northern Europe's largest buildings and consists primarily of limestone from Omberg. Construction was begun in 1819 on 100 hectares of land. The fortress was to house a garrison of 6,000 enlisted men and an additional 8000 to 10 000 people. The walls were mostly complete in 1830, and after comprehensive visits to other fortresses in Europe, fortress architect Johan av Klen presented plans similar in style to the Winiary fortress in Posen (present-day Poznan).
Karlsborg Fortress was built to realize the so-called central defense idea adopted by the Swedish military after the Finnish and Napoleonic Wars. The site was chose by Baltzar von Platen in connection with the construction of Göta kanal. The intent of the central defense idea was that the King, the Council, the Riksdag and central command functions would, in the event of an attack against the kingdom, pull back and ensconce themselves in this fortress in the middle of the country. Even the gold reserves of the central bank of Sweden were to be safeguarded in the fortress in times of trouble.
Due to its great expense and reduced funding, the fortress wasn't in operation until 1870, and wasn't fully completed until 1909. To compensate for the rapidly evolving technology of artillery during this time, Vaberget Fortress was built in the early 1900s five kilometers west of Karlsborg to provide additional protection to the main fortress.
The town of Karlsborg has sprung up next to the fortress. It was initially mostly living quarters for personnel employed at the fortress, but grew to a sizable community, in part due to Göta kanal which passes through the town.
Ever since the fortress lost its intended central defensive rôle in 1918 it has been used as a garrison for Göta signalregemente, S 2, and since 1984 Livregementets husarer, K 3, are also based there.
Karlsborg has been a Swedish listed building in Sweden (byggnadsminne) since 1935. The garrison church is especially worth visiting. The church is housed in the central building of the fortress, 'the last stand', on the second floor above the Fortress Museum. The church was once intended as an assembly hall for the Riksdag in times of troubles. A chandelier composed of bayonets instead of crystal prisms hangs from the ceiling.References:
Varberg Fortress was built in 1287-1300 by count Jacob Nielsen as protection against his Danish king, who had declared him an outlaw after the murder of King Eric V of Denmark. Jacob had close connections with king Eric II of Norway and as a result got substantial Norwegian assistance with the construction. The fortress, as well as half the county, became Norwegian in 1305.
King Eric's grand daughter, Ingeborg Håkansdotter, inherited the area from her father, King Haakon V of Norway. She and her husband, Eric, Duke of Södermanland, established a semi-independent state out of their Norwegian, Swedish and Danish counties until the death of Erik. They spent considerable time at the fortress. Their son, King Magnus IV of Sweden (Magnus VII of Norway), spent much time at the fortress as well.
The fortress was augmented during the late 16th and early 17th century on order by King Christian IV of Denmark. However, after the Treaty of Brömsebro in 1645 the fortress became Swedish. It was used as a military installation until 1830 and as a prison from the end of the 17th Century until 1931.
It is currently used as a museum and bed and breakfast as well as private accommodation. The moat of the fortress is said to be inhabited by a small lake monster. In August 2006, a couple of witnesses claimed to have seen the monster emerge from the dark water and devour a duck. The creature is described as brown, hairless and with a 40 cm long tail.