Gavi was built by incorporating a pre-existing castle built, according to legend, at the time of the Saracen occupations and anointed by Princess Gavia who had established her residence in that location. The first document that testifies to the existence of the castle is a notarial act dating back to the year 973.
The castle remained the property of the Genoese, albeit with ups and downs, at least until 1418 when it passed first to the Milanese Lordship of the Visconti, then to the Fregoso family and finally to the Alexandrian Guasco, lords of Francavilla.
Over the centuries the transformation from castle to fort has been slow but constant: the first radical interventions on the original structure were made in 1540 by the military engineer in the service of the Republic Giovanni Maria Olgiati.Disarmed in 1859, the fort was transformed into a civil penitentiary. During the First World War it was used as a prison camp for the Austro-Hungarians, while during the Second World War it was used as a prison camp for Anglo-American officers. The fortress can be visited in the various main rooms.
References: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.