Karlstens fästning, Stone fortress on Marstrand Island, Sweden
Carlsten Fortress is a stone fortification on Marstrand Island that rises from a rocky hilltop, featuring a circular tower approximately 40 meters tall. Defensive walls surround the central structure, creating a compact defensive complex.
King Charles X Gustav commissioned the fortress in 1658 following Sweden's acquisition of the Bohuslän region through the Treaty of Roskilde. The stronghold was strategically built to defend the newly gained territories.
Carlsten was a prison for men sentenced to penal labour, and Lasse-Maja, its best-known inmate, was held here from 1813 to 1838. Metta Fock is the only woman known to have been imprisoned in the fortress, between 1806 and 1809. Remaining fortress prisoners were moved to Gothenburg's police house in 1888.
The fortress stands on Marstrandsön; the island is reached by ferry from Koön, and buses run from Gothenburg to the ferry. Inside the walls, paths and ramps climb the rock between the tower, the 18th-century buildings and the bastions, so allow time for uneven ground.
The fortress held its last military function until 1993, when the coastal surveillance radar in the tower was removed. Its most famous inmate, Lasse-Maja, was imprisoned here from 1813 to 1838. Metta Fock, held 1806–1809, was the only woman ever imprisoned in this men's fortress.
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