Geoffrey of Monmouth includes Constantine in a section of his "Historia Regum Britanniae" adapted from Gildas. As he does throughout the work, Geoffrey alters his source material, recasting Gildas' reproved kings as successors, rather than contemporaries as in "De Excidio". In addition to Gildas, Geoffrey evidently knew the Dumnonian genealogy essentially as it appears in "Geraint and Enid" and similar sources. He further adds a number of other details not found in earlier sources, identifying Constantine as a son of Cador, a Cornish ruler known in Welsh tradition as Cadwy mab Geraint. Notably, Geoffrey's Constantine is King Arthur's kinsman and succeeds him as King of the Britons. Norris J. Lacy and Geoffrey Ashe suggest Geoffrey made this Arthurian connection based on an existing tradition locating Arthur's birthplace in southwest Britain. However, noting that the earliest references place Arthur in northern Britain rather than the southwest, Rachel Bromwich considers the connection an arbitrary invention by Geoffrey, perhaps suggested by his earlier inventions of familial ties between Arthur and Constantine the Great and the usurper Constantine III. Geoffrey calls Constantine Arthur's "cognatus", or blood relative, but does not specify the exact relation, causing much confusion for later writers.