[Ea]

I nominate Le Morte d'Arthur by Thomas Malory.

From amazon.co.uk:
In a resonant prose style, Malory charts the tragic disintegration of the fellowship of the Round Table, destroyed from within by warring factions. Recounting the life of King Arthur, the knightly exploits of Sir Lancelot du Lake, Sir Tristram, Sir Gawain, and the quest for the Holy Grail, Le Morte Darthur depicts the contradictions that underscore the Fellowship's chivalric ideals. A pervading tension cumulates in the revelation of Lancelot and Guenivere's illicit passion, and in Arthur's powerlessness to prevent a related outbreak of violence and revenge.