Geoffrey of Monmouth, History of the Kings of Britain ((Arthur-and Merlin-excerpts 6.17-8.1, 8.10-8.12, 8.15, 8.17, 8.19-9.16 (skim 9.17-9.19), 9.20-10.9 (skim 10.10-10.13), 11.1-2))