Petrie, George. 1891. “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):71-94. https://journals.socantscot.org/index.php/arch-scot/article/view/313.