Carlstens Fort

Carlsten is a stone fortress located at Marstrand, on the western coast of Sweden. The fortress was built on the orders of King Carl X of Sweden following the Treaty of Roskilde, 1658 to protect the newly acquired province of Bohuslän from hostile attacks. The site of Marstrand was chosen because of its location and its access to an ice free port. The fortress was decommissioned as a permanent defense installation in 1882, but remained in military use until the early 1990s.