thumb|St Michael's Chapel
thumb|Derby Fort
thumb|St Michael's Isle
St Michael's Isle ( or ), more commonly referred to as Fort Island, is an island in Malew parish in the Isle of Man, noted for its attractive ruins. It covers an area of , is about long from west to east, and is connected to the Langness Peninsula, near Derbyhaven, by a narrow causeway. The island itself is made of rocky slate and the soil is very acidic.
History
There is evidence for human activity on the island from the Mesolithic period onwards
In 1275 after Alexander III, King of Scotland, had obtained possession of the Isle of Man, rebellion broke out on behalf of Godred, son of King Magnus, whom Alexander had defeated in battle and who had subsequently ceded the Isle of Man. John de Vesci, a Galloway nobleman, and other officers of the Scottish King landed on St Michael's Isle and again peace was offered and refused. The following morning, prior to sunrise, battle was joined and the Manx were defeated.
Kirk Michael (not to be confused with the Manx village of the same name) is mentioned in a description of the boundaries of Rushen Abbey, which appears to have been compiled in or around the year 1376. "Kirk" is a Scottish and former Northern English word meaning "church", and in this context, is a reference to Michael's Church, now known as St Michael's Chapel in modern English. St Michael's Chapel, a 12th-century chapel, is on the south side of the island. This Celtic-Norse chapel was built on the site of an older Celtic .
The island is the site of two great battles for the control of the Isle of Man in 1250 and 1275, when England, Scotland and the Manx were fighting for control of the island. The Manx won the first battle, but as described above, 25 years later they lost control to Scotland.