Edward Laws, Archaeologia Cambrensis, vol. XII, Londres, Chas. J. Clark, coll. « Fifth Series », (lire en ligne), « Discovery of the Tombstone of Vortipore, Prince of Demetia », p. 303 – 306
Alex Woolf, The Britons: from Romans to Barbarians, p. 371-373 in Hans-Werner, et al.(eds.) Goetz, Regna and Gentes : The Relationship Between Late Antique and Early Medieval Peoples and Kingdoms in the Transformation of the Roman World, , 704 p. (ISBN978-90-04-12524-7 et 90-04-12524-8, lire en ligne)