The sea fortress of Ruotsinsalmi protected the northwestern border of Russia

Russia and Sweden fought in a power struggle for mastery of the Baltic Sea for almost the entire 18th century. Russia wished to strengthen its defence along its northwestern border because of the tense climate remaining after the Russo-Swedish War(1788-1790). Thus, the construction of a fortress chain was begun to protect the then Russian capital of St. Petersburg. The southernmost base of this fortress system became the Ruotsinsalmi sea fortress, and the defensive chain continued to Savonlinna.

The fortresses were built on the islands off Kotka

The islands off the coast of Kotka on the Ruotsinsalmi strait were found to be good places to build defensive fortresses, as the strait's large harbour area and sheltered anchorages were suitable even for a larger naval fleet. These coastline fortifications operated in cooperation with the land-based Kyminlinna fortress.

Construction began around the city of Kotka and on the islands off the coast in the autumn of 1790. The complex consisted of forts, strongholds, fixed gun batteries, and ammunition cellars. Underwater barriers and other structures were built to close off smaller water passages between the straits.

The most important fortresses and the lighthouse of Ruotsinsalmi

Situated on Kukouri Island and completed in 1794, the outermost stronghold was Fort Slava, which is the most important and distinctive of the fortresses. This round fortress was built of stone and brick and had 44 gun stations. The fort was kept armed throughout the Crimean War, until 1855. The ruins have been excavated and were restored in the late 20th century.

An aerial view of Fort Slava.

Built opposite to Kukouri on Varissaari Island, Fort Elisabeth was designed to work with Fort Slava as the main defensive line for sea lanes leading into the Ruotsinsalmi strait. When combined, these forts were able to control the surrounding sea areas with their cannon fire.

Fort Elizabeth was built as an elongated semi-circular fortification, composed of a double-walled defensive perimeter. The foundations of the barracks, gunpowder cellar and warehouse building inside the perimeter are still visible.

Operating as the central fortification on Kotka Island is the dual fortress of Fort Katarina, which was built at the southwestern tip of the island, south of what is today the residential area of Katariina. Large cannons were placed here to control the southwest and western sea areas. Administrative buildings, officers’ quarters and a church were housed within the protection of the fortress.

In 1798, a 24 metre high lighthouse tower was built on the hill of the Katariina Peninsula. It was the second ever lighthouse built in Finland. It served as a harbour lighthouse and as a fixed reference point for the Ruotsinsalmi Fortress and the Russian navy station.

Ruotsinsalmi Lighthouse in the 1840’s. Artist: Pehr Adolf Kruskopf.

The fortifications fell out of use after the Finnish war

After the death of the Russian Empress Catherine II in 1796, her son Paul I came to power, who ended the fortification work in Finland. The defences were mostly complete, with only a few additional structures missing. Although parts of the fortifications were refurbished and supplemented in the early 19th century, by the end of the Finnish War (1808-1809), they were made redundant as the country's border now moved far to the west.

Both the fortresses and the lighthouse were destroyed during the Crimean War in the summer of 1855, when the British Navy entered the Ruotsinsalmi strait. Large quantities of explosives were carried from the ships to the strongholds, which were blown to pieces.

The Ruotsinsalmi strait is full of fortress ruins and remnants

The sea forts on the Ruotsinsalmi strait are a unique part of Finnish fortress history. There are still many ruins and remnants that can be explored around the Ruotsinsalmi area. For example, the Church of St. Nicholas in the centre of Kotka is the only preserved building which dates from the time of the fortress town.

The lighthouse ruins form part of the oldest lighthouse construction in Finland. There is a viewing platform built on top of the ruins, which overlooks the magnificent landscape of Ruotsinsalmi. On the island of Varissari, among the ruins of Fort Elizabeth, are artifacts recovered from the sunken frigate Sankt Nikolai and a war memorial commemorating the Second Battle of Svenskund (1790). Today, this area belongs to the Katariina Seaside Park.

There are many shipwrecks in the waters of the Ruotsinsalmi strait, which you can learn about in the cultural environmen service window. 

Why and how is this location protected?

The Ruotsinsalmi fortresses are rare, forming a group of isolated forts built over a large area with scattered gun battery units located on the islands between them. The Finnish Heritage Agency has designated these fortified areas as nationally significant built cultural environments. In addition, the individual fortress sites and the lighthouse ruin are protected by the Antiquities Act.


Both Fort Katarina and the observation tower can be explored on foot. Varissari Island can be visited in summer on a boat operated by the owner of the summer restaurant there. Kukouri Island is only accessible by charter boat. Both islands can also be reached by private boat.

Explore boat transportation options on visit Kotka-Hamina webpage. 

Finnish Heritage Agency’s mapservice:

N: 6702296, E: 498185 (ETRS-TM35FIN) (central coordinate point)