St David's Church was founded in 1187, built on the site where a famous synod was held in the sixth century. According to local legend, it is said that during this synod, which St David addressed, the flat ground rose into a mound beneath his feet, allowing him to be better seen and heard by the vast crowd that had gathered to hear him speak. The church supposedly stands on that same mound. It's possible that, in reality, it was built on the site of a Bronze Age barrow.
The central tower dates from the 12th century, which, in medieval times, had five bells in its belfry. Today there is only one bell, which was given to the church by John Inglis Jones of Derry Ormond in 1874. The 12th century nave and chancel were taken down in 1832, being beyond repair, and replaced in 1833–34. The new building was of poor quality, however, and the nave as it stands today was rebuilt in 1874, and the Chancel in 1886.
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.