The construction of Gerione Castle was probably motivated by the need to control mountain routes and its strategic position as an observation point for a large part of the Sele plain. Documented for the first time in a parchment from 1056 during the Lombard period, the exact date of its construction is unknown.
With the Assise of Capua in 1220, the Gerione Castle was acquired by Frederick II of Sweden for the Demanio Regio, becoming directly dependent on the emperor and included among the Castra exempta, the main fortifications of the kingdom.
The structure maintained its military-defensive function until 1515 when, due to its inconvenient location for the needs of the time, it was handed over to the Collegiate Church of Santa Maria della Pace by the last feudal lord to possess it, Duke Ferdinando Orsini. According to others, the castle was used both as a prison and as a Spanish garrison during the feudal rule of the Grimaldi Princes of Monaco, Marquises of Campagna.
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.