Excalibur: A Novel of Arthur:The Warlord Chronicles 3 by Bernard Cornwell
A story of love, war, loyalty and betrayal, EXCALIBUR begins with the failure of Lancelot's rebellion and the ruin of Arthur's marriage to Guinevere. The Saxons, sensing the disunity of the Britons, seize the chance to destroy Arthur. The climax of the war comes with the legendary triumph at Mount Badon, and Arthur's great victory. But the promises he made then come back to haunt him after the years of peace and glory.