The sea fortress of Suomenlinna is situated off the coast of Helsinki in the waterway of the Gulf of Finland, midway between Turku and Vyborg.

1747 Sweden decides to fortify six islands known as the Susiluodot off Helsinki.

1750 The sea fortress is called Sveaborg, which is rendered in Finnish as Viapori.

1748-1772 The first stage of construction of Viapori is carried out under Colonel, later Field Marshal Augustin Ehrensvärd. The fortification technique is modelled on the bastion system developed by Field Marshal Sebastian le Preste du Vauban of France.

1772-1808 Sweden expands the fortress of Viapori.

1808 Russia overruns Viapori and establishes a garrison.

1854-1917 Russia installs artillery batteries on top of the Swedish bastion fronts. The fortress, Sveaborgskaja krepost, expands to the outer islands off Helsinki. In the First World War it forms the central part of a maritime defence system named after Peter the Great.

1918 Viapori is given the official Finnish name of Suomenlinna.

1919 The islands Kustaanmiekka and Susisaari are declared historical monuments and renovation work begins.

1952 During the Helsinki Olympics connections between Suomenlinna and Helsinki improve with the entry into service of a new civilian ferry. A restaurant (Walhalla) is opened in the renovated fortification works of Kustaanmiekka.

1973 Suomenlinna is transferred to civilian administration. The Naval Academy continues, however.

1975 A plan for the usage of Suomenlinna is drawn up.

1991 Suomenlinna is listed as a Unesco World Heritage Site.

1998 250th anniversary, tourist services upgraded, new Visitor Centre opened. 600,000 people visit Suomenlinna each year.

2002 regulations for organizers of events in Suomenlinna published.

Today Suomenlinna is a part of the city of Helsinki. It is entirely owned by the state and is administered by the Governing Body of Suomenlinna, which operates under the Ministry of Education and has around 800 tenants resident on the islands. The Suomenlinna labour colony, which operates under the Ministry of Justice, renovates the fortifications and buildings.

Suomenlinna is one of Finland's principal tourist attractions, with the Suomenlinna Museum, the Ehrensvärd Museum, the Military Museum and the submarine Vesikko, the Customs Museum, the Doll and Toy Museum and a summer theatre. Some of the buildings have been restored as art and craft studios. The galley dockyard is 250 years old and is used for the renovation of wooden boats. Suomenlinna has several restaurants and cafés. In summer concerts and cultural events are held and there are guided tours.