With his single foray into Arthurian legend, he may well have achieved his finest accomplishment by bringing to bear the transforming perceptions of the old narratives a pervasive sense of the grave and fateful nature of all that is told in The Fall of Arthur. of Arthur’s expedition overseas into distant heathen lands, of Guinevere’s flight from Camelot, of the great sea battle on Arthur’s return to Britain, in the portrait of the traitor Mordred, in the tormented doubts of Lancelot in his French castle.
The Fall of Arthur was one of Tolkien's abandoned long narrative poems. A friend read it with great enthusiasm at the end of 1934, and asked him to finish it as soon as possible, which he eventually did, though it may have been in 1937, the year of the publication of The Hobbit and the beginnings of The Lord of the Rings. Years later, in a letter of 1955, he said that he "hoped to finish a long poem on The Fall of Arthur," but that day never came.
However, it has many manuscript pages associated with it: a lot of drafting and experimentation in verse, revealing the strange development of the poem's structure, in addition to several narrative synopses and tantalizing notes. The notes reveal clear, although mysterious associations between the Arthurian conclusion and The Silmarillion, as well as the bitter end of the love story between Lancelot and Guinevere that was never written.