Carlsten, located in the municipality of Bohuslän on the island Marstrandsёn, in the 19th century was known throughout the world as one of the strongest and most fortified in Europe.

Once in 1658, peace was concluded in Roskilde, Bohuslän went to Sweden. The city has long been a major trading center, but due to the fact that the port during the year virtually never freezes, located here and a part of the Swedish navy. To protect Marstrandsёn, Charles X decided to build fortifications on the island. Develop a project of the future fortress was entrusted to engineer Johan Vernshёldu. Initially, in 1658 on the island were built makeshift wooden fortifications, thanks to which in 1659 the Swedes managed to repel the attack of the Norwegian troops. In 1666 it began the construction of a stone fortress. In the years 1780-1783 were carried out construction work in the tower KarlsTom, on the basis of which it could also serve as a lighthouse. Moreover, it was the first lighthouse in the world with rotating mirror device.

Almost from the first years of its existence Carlsten served as a prison for political prisoners, and for especially dangerous criminals. For example, here for 26 years it kept the most famous Swedish adventurer robber and Lasse Maya. Despite the fact that by 1855 all prisoners moved to Gothenburg, KarlsTom has long been a known popularly as the "fortress of prisoners."

Due to the fact that in the second half of the 19th century steam marine vessels sailing almost completely replaced, and the war with Denmark became less likely, the importance Carlsten plummeted. That is why it was decided to transfer the artillery regiment of KarlsTom in Vakskholmskuyu and Karlsborgskuyu fortress. In the years 1906-1937 the premises of the fort was in use Marstrandskoy school apprentices. Using a fortress for defensive purposes it was finally discontinued in 1993.