The study of Geoffrey's book and of the allied Welsh texts is a subject of such complexity, and has produced such a mass of technical literature, that the intrusion of a newcomer into these jealously guarded preserves of recondite scholarship is naturally liable to direct at once the cold stare of disapproval, or at best the wan smile of tolerance upon one so rash. I am not unmindful that in a previous world-conflict Sir (Emeritus Professor) Flinders Petrie put forward views on the Historia from an outsider's standpoint which were instantly demolished in a few quietly incisive notes by Professor R. W. Chambers. But, despite the vast tangle of adherent commentary which now envelops Geoffrey's book to an extent that all too often dwarfs the actual text, it seems likely that certain basic questions—is it a work of fiction or of fact, or if both, in what proportions—should be answerable to some extent by enquiring whether certain passages read convincingly as sheer invention, and if not, what prevented the author from making them so. I hope to show that one can trace in the Historia a use of certain documentary sources which to the best of my knowledge have not been recognized in full before. I venture therefore to put forward these tentative ideas in the hope that they may be followed up or refuted by those more qualified for the task than myself, examining the problem for the first time and from the outside, and in those enforced circumstances in which the only really accessible works of reference are the King's Regulations and the Manual of Military Law. As a contrast it is a pleasure to record my thanks to those who have aided me, notably Professor Ifor Williams, who has given me invaluable advice and helped to eradicate the more egregious errors from my argument.