The Tour des Archives is the keep of a former castle. Its origin goes back to 1123, built by King Henry I of England, the son of William the Conqueror. It is 22m high and is a rare existing example of a round tower in Normandy, like the so-called tour Jeanne d'Arc (Joan of Arc Tower) of the former Rouen Castle. The Tour des Archives has been classified since 1840 as a monument historique by the French Ministry of Culture.
References:Bomarsund fortress and garrison was built in 1832-1854 by Russian Empire to defence Åland Islands against enemies. British and French fleet attacked against it during the Crimean War in 1854. After a week of fighting the British stormed the remaining fort. Anglo-French forces destroyed it totally after battle. In the Treaty of Paris 1856, the entire Åland Islands were demilitarized, which is a status that has been preserved until this day.
Nowadays there are some ruins left and fortress area is open for visitors.