Robertson, Thomas. 1832. “Letter from Thomas Robertson, Esq., to the Earl of Buchan, Respecting the Discovery of a Stone Coffin at Arbroath, Supposed to Contain the Remains of King William the Lyon”. Archaeologia Scotica 3 (November):297-98. https://journals.socantscot.org/index.php/arch-scot/article/view/240.