The steep plateau of Saint-Blaise oppidum is accessible only from the south, therefore easy to defend, was inhabited from the Neolithic until the end of the 14th century with a long interruption during the High Roman Empire (from the 1st to the beginning of the 4th century AD). The excavations undertaken by Henri Rolland in 1935 and continued after his death, have brought to light eight archaeological layers.
There are today remains of Hellenistic rampart (2nd century BC), surmounted by the early Christian walls, a Christian necropolis, and foundations of 11th century church. The Chapelle St-Blaise is a 12th century Romanesque building, restored in the 13th century and whose facade was redone in 1608.
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.