Rosemary Sutcliff 
The Road To Camlann 

Rooted in folklore, medieval ideals of chivalry, and the last gallant struggles of the British against the Saxon invaders, the legends of King Arthur have been told in song and story since the middle ages.
The best and noblest of Arthur»s Knights lost in pursuit of the Grail, the shining days of Camelot draw to their tragic close — and Arthur»s son and doom Mordred leads him to the last desperate battle against the coming of future darkness.