The Brough of Birsay is an uninhabited tidal island off the north-west coast of Mainland in Orkney, Scotland. The island is only accessible at low tide via a natural causeway. The word 'brough' or 'broch', means fort. The small island has a rich history. The earliest settlement is believed to date back to the 6th century, possibly established by Christian missionaries. During the 7th and 8th centuries, it served as a Pictish stronghold. By the 9th century, it was occupied by Norse settlers.