Following the war of 1808–09, Russia began building this major military structure as its westernmost defence against the Swedes. The fortress was still incomplete when the Crimean War began in 1854, and a French-British naval force bombarded it heavily from the sea. Within four days the Russians were forced to surrender it. The evocative ruins stretch for a couple of kilometres, straddling the road and overlooking the sea. Across the water on Prästö, the small Bomarsund Museum displays excavated artefacts.