When we got off the ferry in Helsinki, the crisp 17°C air was a welcome change from the heatwave we’d left behind at home. After a short walk around the city, we decided to take another ferry – this time to Suomenlinna, a former sea fortress spread across several small islands just off the coast. Its history turned out to be far more complex than I’d expected: originally built by the Swedes, later taken over by the Russians, used as a prison after Finland’s civil war, and then again as a military base during the Second World War. These days, Suomenlinna is a peaceful spot popular with both tourists and locals – part open-air museum, part quiet park, with plenty of space to wander, sit by the water, or simply take in the surroundings.
Finland’s Historic Sea Fortress Suomenlinna | フィンランドの歴史的な海の要塞スオメンリンナ | 芬兰的历史海上要塞芬兰堡 | 핀란드의 역사적인 해상 요새 수오멘린나 | Fortaleza histórica marítima de Finlandia, Suomenlinna | Forteresse maritime historique de Finlande, Suomenlinna | Finnlands historische Seefestung Suomenlinna | Fińska historyczna twierdza morska Suomenlinna
About a year ago, we took a ferry trip from Tallinn, Estonia, to Helsinki, Finland. We had around 10 hours to explore Helsinki. Although it was a heatwave back home, the temperature in Helsinki was about 17 degrees Celsius. The weather was quite pleasant, so after a brief walk around the city, we decided to take a ferry to Suomenlinna. This was my first encounter with Finland. While I have a decent understanding of Central and Western European history, I realised that in seeking information about this place, I am essentially learning Finnish history from scratch.
Suomenlinna is a sea fortress located on several islands off the coast of Helsinki. Also known by its Swedish name, Sveaborg (meaning Swedish Fortress), it was constructed in the 18th century when Finland was part of the Kingdom of Sweden. The fortress aimed at securing the kingdom’s eastern borders against Russian expansion. Suomenlinna, covering around 80 hectares across six islands (Kustaanmiekka, Susisaari, Iso Mustasaari, Pikku Mustasaari, Länsi-Mustasaari, and Långören), was one of the largest defensive projects in Europe and the world at the time, influenced by French fortification techniques. Suomenlinna served as the main base for the Swedish fleet in the eastern Baltic, strategically positioned at the entrance to Helsinki, making it a critical point in Sweden’s defence.
In the early 19th century, Europe was engulfed in the Napoleonic Wars. Sweden, a traditional adversary of Russia, faced a difficult geopolitical situation. In 1807, Russia, allied with France, demanded that Sweden join the continental blockade against Britain. When Sweden refused, Russia invaded Finnish territories under Swedish control. The Russian forces swiftly advanced westward, and in March 1808, they began the siege of Suomenlinna, cutting off the fortress from the rest of Sweden by sea. Despite its strong defences, the fortress’s garrison of about 6,000 soldiers faced dwindling supplies and uncertainty about further support from Sweden.
Admiral Carl Olof Cronstedt, the commander of the fortress, was under immense pressure. Morale among the soldiers was low, and supplies were running out. Realising that a prolonged siege could lead to starvation and disaster, Cronstedt decided to negotiate with the Russians. The Russian forces were well-prepared to continue the siege but were also open to negotiations to avoid unnecessary bloodshed. After weeks of talks and growing pressure from his own officers, Cronstedt eventually decided to surrender the fortress. On 3 May 1808, after brief negotiations, a surrender agreement was signed. The terms were relatively lenient – the garrison was allowed to leave with honours, and the Russians took control of the fortress without major damage. The surrender of Suomenlinna was a significant blow to Sweden, effectively deciding the outcome of the war. It opened the way for further Russian expansion into Finland. After the surrender, Russia quickly took control of the rest of Finland. Finland was officially annexed to the Russian Empire as an autonomous Grand Duchy. Under Russian rule, the fortress was expanded and modernised. The Russians added new fortifications and storage facilities to meet modern defensive needs, incorporating new military architecture and technology into the existing Swedish structures. The fortress also served as a military base and a prison for political prisoners.
After Finland declared independence in December 1917, the country was deeply divided, leading to civil war between the Whites and the Reds, each with different visions for Finland’s future. The Whites were conservative republicans, mainly from the middle class, landowners, the bourgeoisie, and officers, supported by wealthier farmers and intellectuals. They sought to establish a strong, independent Finnish state based on national and republican values, while maintaining traditional social and economic structures. They received crucial support from Germany, including military equipment, advisors, and troops. The Reds were a socialist and leftist movement drawn from the working class, poorer farmers, and radical intellectuals. They represented those who experienced deep social inequality and sought radical reforms to create a more just society. They aimed to establish workers’ rule and a socialist economic system inspired by the Russian Revolution of 1917, advocating for the state takeover of property, broad workers’ rights, and political reforms.
Suomenlinna played a key role in these events. During the civil war, it was seized by the Whites and used as a military base and stronghold. After the Whites won the conflict in May 1918, Suomenlinna was turned into a prisoner-of-war camp, holding mainly Red soldiers and those suspected of supporting the socialist movement. The camp’s harsh conditions, overcrowding, lack of food, and medical supplies led to high mortality among the prisoners. A place once symbolising resistance and strength had become a site of suffering and tragedy.
During World War II, Suomenlinna again served a military role, acting as a base for Helsinki’s air defence and a command post. Its strategic location at the capital’s entrance made it a critical element in Finland’s defence against Soviet bombings.
Finland’s Historic Sea Fortress Suomenlinna | フィンランドの歴史的な海の要塞スオメンリンナ | 芬兰的历史海上要塞芬兰堡 | 핀란드의 역사적인 해상 요새 수오멘린나 | Fortaleza histórica marítima de Finlandia, Suomenlinna | Forteresse maritime historique de Finlande, Suomenlinna | Finnlands historische Seefestung Suomenlinna | Fińska historyczna twierdza morska Suomenlinna
Today, Suomenlinna is known for its diverse architecture, reflecting its long history and the influences of various powers. The fortress includes many bastions, defensive walls, forts, and historic buildings, such as warehouses, barracks, and workshops. It is not only a tourist attraction but also a residential area with about 800 inhabitants. The fortress hosts numerous cultural events, including concerts, exhibitions, and festivals. Besides its historical significance, Suomenlinna offers beautiful landscapes. The fortress is easily accessible from central Helsinki, with regular ferries departing from Kauppatori square. In summer, tourist cruises also offer the chance to admire the fortress from the sea.
