Suomenlinna (Sveaborg) is a sea fortress built gradually from 1748 on a group of islands belonging to the Helsinki Region. The work was supervised by the Swedish admiral Augustin Eherensvärd (1710–1772).
The landscape and architecture of the fortress have been shaped by several historical events. Over the years it has served in the defense of three different sovereign states: the Kingdom of Sweden, the Russian Empire and most recently the Republic of Finland.
The fortress covers an area of 210 ha, consists of 200 buildings and 6 km of defensive walls, and is spread over six separate islands. The original fortress was built of local stone and fortified with a system of bastions on varied terrain. The purpose of the fortress was originally to defend the Kingdom of Sweden against the Russian Empire and to serve as a fortified army base with a dry dock. Sandbanks, barracks and various other buildings were added during the 19th century Russian period. The defense system was adapted to the needs of a modern fortress and further developed in the 19th century using contemporary fortification equipment.
After Finland's independence in 1917, the fortress was renamed Suomenlinna (or Fortress of Finland) and served as a garrison and port. After the Second World War, the military importance of the fortress decreased and in 1973 the area was converted for civilian use. Since then, buildings have been refurbished for use as both dwellings and workspaces, to house private and public services, and for cultural purposes.
Today Suomenlinna is one of Finland's most popular tourist attractions and forms a district of Helsinki with 850 inhabitants.