Petrie, George. “Notice of the Brochs or Large Round Towers of Orkney, With Plans, Sections, and Drawings, and Tables of Measurements of Orkney and Shetland Brochs”. Archaeologia Scotica 5 (November 30, 1891): 71-94. Accessed September 25, 2022. http://soas.is.ed.ac.uk/index.php/arch-scot/article/view/313.