"Duke of Cornwall" appears as a title in pseudo-historical authors such as Geoffrey of Monmouth. The list is patchy and not every succession was unbroken. Indeed, Monmouth repeatedly introduces Dukes of Cornwall only to promote them to the Kingship of the Britons and thus put an end to their line as (merely) dukes. As adjuncts or supporting roles to the kings of the Britons, the legendary dukes of Cornwall are considered part of the vast Matter of Britain, and can also be found in other stories, such as Culhwch and Olwen, the Prose Tristan, Havelok the Dane, and Gesta Herewardi. Antiquaries such as Richard Carew (Survey of Cornwall, 1602) and John Williams (the Book of Baglan, 1600–1607) also provide lists of legendary rulers of Cornwall, often combining the above with other sources.