The Russian era

In 1808, Viapori surrendered to the Russians, and the fortress was taken over by the Russian Imperial government. In the following year, Finland became an autonomous Grand Duchy in the Russian Empire, but Viapori remained a Russian military base.

The Russians held the fortress in high regard and had big plans for it. They expanded the fortress perimeter to further islands: Santahamina, Kuningassaari and Vallisaari. However, during the Russian era Viapori became more of a garrison than a fortress, and its military strategic importance declined as the 19th century progressed. Huge barracks were built to house soldiers. By contrast, care and rebuilding of the fortifications were neglected due to a lack of funds, and parts of Viapori fell into decay.

It was not until the run-up to the Crimean War (1853–1856) that the condition of the fortress began to raise concerns. Though the war broke out between Russia and Turkey, England and France soon joined forces with the Turks. A combined Anglo-French fleet bombarded Viapori for two days in August 1855. At this point, the repair work was nowhere near complete, and Viapori sustained heavy damage in the bombardment.

In the late 19th century and the early years of the 20th century, the fortifications of Viapori were built up again. However, Viapori continued to decline in importance, and ultimately it was just one Russian fortress among many.

In summer 1906, inspired by revolutionary unrest in Russia, a military rebellion erupted on Viapori. The mutineers attempted to bring the fortress under their control and very nearly succeeded. However, the rebellion was quashed four days later.

During the First World War (1914–1918), Viapori formed part of what was known as the Naval Fortress of Peter the Great, designed to protect the Russian capital of St Petersburg. With the Russian Revolution and Finland’s independence, Viapori was taken over by the newly founded Finnish government in 1918 and renamed Suomenlinna.