Suomenlinna: A Historic Sea Fortress in Helsinki, Finland
Site at a Glance
- Rating
- 4.6
- Popularity
- Very High
- Country
- Finland
- Primary era
- Early Modern
- External website
- Open
- Eras represented
- Early Modern, Modern
- Civilizations
- Russian, Swedish
- Site type
- Military
- Remains
- Fort
On this page16 sections
History
Suomenlinna is an eighteenth-century sea fortress in Helsinki, Finland, established by the Swedish Crown in 1748 to defend the Finnish coast and Helsingfors, the Swedish name for Helsinki, against Russia. Built as both an island fortress and a naval base for Sweden’s archipelago fleet, a shallow-draft force intended for island and coastal waters, it became one of the major military projects in the eastern Baltic.
Swedish foundation and construction
Sweden began the project after the Russo-Swedish War of 1741 to 1743 had exposed the weakness of Finland’s coastal defenses. Sweden also lacked a suitable naval base in the eastern Baltic. The new fortress was intended to counter the Russian naval base at Kronstadt, support Swedish operations in Finland, and store munitions for the Swedish army and navy.
Augustin Ehrensvärd, a Swedish military officer and military architect, directed the design and construction. Work started in early 1748, with soldiers and other workers forming the main labor force. More than 6,000 people were employed in 1750, and the workforce reached about 7,000 in 1755.
Ehrensvärd planned independent fortifications across linked islands, a central naval dockyard, and defenses on the mainland designed to prevent an attacking force from establishing a beachhead. The southern island fortification of Gustavssvärd, later known as Kustaanmiekka, was completed in 1751. The principal works on Susisaari were ready in 1754, but the fortress remained unfinished. Sweden’s participation in the Seven Years’ War halted the main construction phase in 1757.
Political change and naval development
Swedish political shifts repeatedly affected the project. Ehrensvärd lost his post in 1766 when the Caps came to power. After the Hats regained power in 1769, he returned to command the Swedish archipelago fleet in Finland, but died in 1772 before the fortifications were complete. Construction continued intermittently under Jacob Magnus Sprengtporten, although disputes with King Gustav III and reductions in the garrison slowed progress. In 1776, the commander reported that fewer than one-tenth of the fortress artillery could be manned, and the works were still incomplete in 1788.
Known in Swedish as Sveaborg and in Finnish as Viapori, the fortress also developed into a center for shipbuilding and naval training. Facilities for constructing vessels for the archipelago fleet were built during the 1760s, and the first three archipelago frigates were launched there in 1764. Ehrensvärd began training naval officers at his own expense in 1770, followed by the foundation of a formal naval military school in 1779.
The fortress was designed primarily for the archipelago fleet. Its position in the surrounding waters could be disrupted by Russian control, which repeatedly restricted the Swedish fleet’s movement and its connection with Sweden. The naval facilities were intended for the island fleet, while the Swedish battle fleet required repair, refitting, and medical arrangements of a different kind.
Russian conquest and rule
During the Finnish War of 1808 to 1809, the conflict in which Russia conquered Sweden’s Finnish territories, Russian forces besieged Sveaborg in 1808. After about two months, the fortress surrendered. Almost 7,000 men, more than 2,000 guns, large supplies, and 110 military vessels passed to the Russians. The surrender helped Russia seize Finland in 1809 and establish the autonomous Grand Duchy of Finland within the Russian Empire.
Under Russian rule, Sveaborg became a Russian military fortress and naval base. The Russians added barracks, enlarged the dockyard, strengthened the existing defensive lines, and later incorporated the fortress and surrounding islands into Peter the Great’s naval fortification. This wider defensive system was intended to protect Saint Petersburg and the Gulf of Finland.
During the Crimean War, fought from 1853 to 1856 between Russia and an alliance that included the Ottoman Empire, Britain, and France, an Anglo-French fleet bombarded Sveaborg on 9 and 10 August 1855. The attack lasted about 47 hours and badly damaged the fortress, although its Russian guns were not destroyed and the fleet did not land troops. Extensive restoration followed, including new earthworks and artillery positions along the western and southern edges of the islands.
By the early twentieth century, the fortress contained a Russian naval station, docks, arsenals, barracks, a naval school, powder magazines, freshwater reservoirs, and an Orthodox military church. The Sveaborg Rebellion took place there in 1906. During the First World War, the islands formed part of the Krepost Sveaborg defense system around Helsingfors. New coastal batteries were placed on outlying islands, while fortified landward lines protected the Russian Baltic Fleet base and the approaches to Saint Petersburg. Construction largely stopped in 1917 after the Russian revolutions, before the system was complete.
Finnish control and twentieth-century military use
After Finland declared independence in 1917, the fortress became involved in the Finnish Civil War. Russian forces handed part of it to the Finnish Red Guard, the socialist and revolutionary armed force, in March 1918. Finnish White forces, representing the opposing government-aligned side and supported by German troops, captured it in early April. The fortress was officially renamed Suomenlinna in 1918, although the Swedish name Sveaborg continued in Swedish.
In 1918 and 1919, Suomenlinna held a prison camp for captured Red Guard soldiers. More than 1,000 of approximately 10,000 prisoners died from hunger and disease, and 80 prisoners were executed.
Under Finnish control, the fortress served as a garrison for a coastal artillery regiment, the Naval Academy, and mine-sweeping vessels. During the Winter War, Finland’s 1939 to 1940 war against the Soviet Union, it housed anti-aircraft and artillery units and served as a submarine base. During the Continuation War, Finland’s 1941 to 1944 war against the Soviet Union while aligned militarily with Germany, Suomenlinna sustained bombing damage and hosted German military forces and naval units from 1941 to 1944.
An ammunition store exploded in 1937, killing 12 people. Finnish artillery remained in use at the fortress until the end of the Second World War. After the war, some island batteries were transferred to the Soviet Union and later returned to Finland.
Shipbuilding, civilian administration, and heritage
The Valmet Shipyard at Suomenlinna built barges and trawlers as Finnish war reparations, constructed vessels for the Finnish Navy and Coast Guard, and repaired ships. For the fortress’s bicentenary in 1948, the courtyard of Susisaari Castle and Kustaanmiekka were restored.
Suomenlinna remained under Finland’s Defence Department until 1973, when most of the complex passed to civilian administration. An independent Governing Body of Suomenlinna was established to manage the site, while the Finnish Naval Academy continued to occupy part of Pikku Mustasaari. UNESCO inscribed Suomenlinna as a World Heritage Site in 1991 under criterion iv, which recognizes an important example of a building type, architectural ensemble, or landscape illustrating a significant stage in human history.
The former fortress is now also a residential district of Helsinki. Its continuing uses include museums, cultural facilities, a minimum-security penal labor colony, and the Naval Academy. Prisoners at the penal labor facility take part in maintaining and reconstructing the historic fortifications.
Remains
Suomenlinna occupies approximately 80 hectares across eight islands southeast of central Helsinki. Six islands are fortified. Five principal islands are joined by bridges, causeways, or filled land, creating a connected chain from Länsi-Mustasaari through Pikku Mustasaari and Iso Mustasaari to Susisaari and Kustaanmiekka. The former waterway between Susisaari and Kustaanmiekka was filled during the Russian period. Särkkä, Lonna, and Pormestarinluodot remain separate from this connected group.
Island fortifications and defensive landscape
The fortress follows a bastion system adapted to rocky islands. Bastions are projecting angular works that allow defenders to cover walls and approaches with overlapping fire. At Suomenlinna, independent island defenses, interlocking positions, sea-facing works, artillery emplacements, ramparts, and the naval dockyard formed a connected military plan. The design drew strongly on the principles of Sébastien Le Prestre de Vauban, the influential French military engineer whose seventeenth-century fortresses emphasized layered defenses and mutually supporting artillery, but it was adjusted to Finland’s archipelago terrain.
Kustaanmiekka and the King’s Gate
Kustaanmiekka is the southernmost island in the connected group. A narrow isthmus links it to Susisaari, and a defensive rampart crosses this connection. Because of the filled and fortified link, Kustaanmiekka is technically a peninsula. Gun bastions and the King’s Gate occupy its southern end, while several small pools lie in hollows in the central bedrock.
Susisaari fortifications
Susisaari, one of the islands associated with the name Wolf Skerries, contains a particularly dense concentration of bastions. It lies between Kustaanmiekka and Iso Mustasaari. A narrow strait separates it from Iso Mustasaari, and a wooden bridge crosses the gap. The courtyard of Susisaari Castle was restored for the fortress’s bicentenary in 1948.
Iso Mustasaari and the northern islands
Iso Mustasaari is the most densely built part of the former garrison. Its surviving buildings and facilities include the church, fortress museum, toy museum, main harbor, residential buildings, and service structures. A planned baroque square, partly modeled on Paris’s Place Vendôme, was only half completed. Many later residential buildings follow the lines and contours of the fortifications.
Pikku Mustasaari and Länsi-Mustasaari lie northwest of Iso Mustasaari. Bridges connect Pikku Mustasaari with both neighboring islands. Most of Pikku Mustasaari is occupied by the Finnish Naval Academy, while its civilian area is concentrated mainly along a street on the southeastern coast leading toward Iso Mustasaari and Länsi-Mustasaari.
Dockyard, barracks, and later defenses
The original plan placed a central naval dockyard among the island defenses. Russian-period works enlarged the dockyard, added barracks, and strengthened existing defensive lines. After the Crimean War, a ring of earthworks with artillery emplacements was built along the western and southern edges of the islands. These works form part of the later defensive layers alongside the earlier Swedish fortifications.
First World War defenses extended beyond the old fortress. New coastal-artillery batteries were installed on distant islands, and fortified landward lines were built beyond the original island group. The system included artillery positions intended to protect the naval base and the approaches to Saint Petersburg. The islands retain numerous historical artillery pieces, including a six-inch Russian siege gun manufactured in 1904 and an 11-inch, or 280-millimeter, gun made at the Perm Steel and Cannon Works in 1870.
Church, museums, and surviving buildings
Suomenlinna Church
Suomenlinna Church was built in 1854 as a Russian Orthodox garrison church. In 1929 it was adapted to incorporate a lighthouse beacon. Both the church and beacon remain active, and the beacon received LED lighting in 2019.
Museums and the submarine Vesikko
The fortress contains the Suomenlinna Museum, Ehrensvärd Museum, Toy Museum, Military Museum Manege, and Customs Museum. The submarine Vesikko is also preserved within the fortress. Together, these facilities occupy part of a landscape that retains military, residential, naval, and cultural uses.
Former school and service infrastructure
A building constructed in 1908 passed through several uses. It was a Russian school from 1909 to 1917, a military office from 1918 to 1919, a Finnish school from 1920 to 1959, and a canteen and entertainment venue for soldiers from 1959 to 1972. It now houses a hostel. A service tunnel built in 1982 supplies heating, water, and electricity; in the early 1990s, it was modified for emergency transport.
The physical and cultural landscape includes courtyards, bastions, artillery positions, dockyard installations, barracks, defensive walls, earthworks, churches, museums, and the rocky island terrain on which the fortress was built. A memorial plaque installed in 1987 commemorates the birth at Suomenlinna in 1811 of Vissarion Belinsky, a Russian humanist and literary critic.
Nearby sites
