After the Sweden's defeat in Russo-Swedish War 1741-1743 (also known as the Hats' Russian War) eastern border of Finland was moved to west. Important fortresses of Hamina, Lappeenranta and Savonlinna were left to Russian side of border.
The city of Loviisa was established in 1745 to handle a international commerce in Finland. Planning of the new fortification system started concurrently, because Loviisa was located alongside the strategic road from Vyborg to Turku. The parliament accepted the plan of twin fortresses in 1747: one in Loviisa city to protect the road and another to Svartholma island to defence Loviisa from the sea. Building of the Loviisa fortress started in 1748, but the plans were never completed. The ground was too muddy for heavy stone walls and the Crown had continuous lack of money. Building was interrupted in 1757 and the king Gustav III ordered to stop the construction permanently in 1775. Loviisa fortress didn't see any battle. In the Finnish War 1808-1809 it surrended to Russians without fighting, because people of Loviisa were afraid of the destruction of the city.
Nowadays there remains two completed bastions, Rosen and Ungern. Renovation started in the 1960's and Ungern is mostly renovated. Rosen is still uncompleted and mostly ruined.
Towering 52 meters above the sea, Bengtskär lighthouse is the tallest one in Scandinavia. The building started in in 1905 after the shipwreck of S/S Helsingfors and was completed in 1906. The lighthouse was designed by architect Florentin Granholm. On December a special petrol lantern, designed and built in Paris, was brought to Bengtskär and installed atop the tower.
German fleet bombarded Bengstkär in the First World War in 1914. Since the Gulf of Finland was heavily mined, it was not until 1919 that the surrounding seas were declared safe for shipping, that the light was lit again.
After the war the military value of Bengtskär increased as part of the defence system of independent Finland. In Second World War (1941) Soviet Union made a suprise attack to island. After a bloody battle, the small Finnish garrison emerged victorious. Intermittent repairs to the facility continued during the post-war period.