Following a romantic escapade in Russia during 1910, Bax married on the rebound and set up house on the outskirts of Dublin, remaining there until the outbreak of the Great War brought him back to London, where he soon fell in love with the beautiful young piano student Harriet Cohen. In August 1917 the couple spent an idyllic six-week holiday at Tintagel, on the north coast of Cornwall, and this experience inspired Bax to compose a tone-poem that was to become the best known of all his orchestral works. Although he wrote it out immediately on his return to London (the draft score is inscribed 'Oct 1917'), he delayed orchestrating it, and the final manuscript dates from January 1919. It bears the dedication 'For Darling Tania with love from Arnold', Tania being Harriet's pet name; but when the work was later published, this had become the more demure 'To Miss Harriet Cohen'. The first performance was given by the Bournemouth Municipal Orchestra under Dan Godfrey on 20 October 1921, and Bax wrote a note describing the piece:

'This work is only in the broadest sense programme music. The composer's intention is simply to offer a tonal impression of the castle-crowned cliff of (now sadly degenerate) Tintagel, and more especially of the long distances of the Atlantic, as seen from the cliffs of Cornwall on a sunny, but not windless, summer day. The literary and traditional associations of the scene also enter into the scheme. The music opens, after a few introductory bars, with a theme, given out by brass, which may be taken as representing the ruined castle, now so ancient and weather-worn as to seem an emanation of the rock upon which it is built. The subject is worked to a broad diatonic climax, and is followed by a long melody for strings, which may suggest the serene and almost limitless spaces of the ocean.

After a while a more restless mood begins to assert itself, as though the sea were rising, bringing with it a new sense of stress, thoughts of many passionate and tragic incidents in the tales of King Arthur and King Mark and others among the men and women of their time. A wailing chromatic figure is heard, and gradually dominates the music until finally it assumes a shape which recalls to mind one of the subjects of the first Act of [ Wagner's ] 'Tristan and Isolda' (whose fate was, of course, intimately connected with Tintagel). Here occurs a motif which may be taken as representing the increasing tumult of the sea. Soon after there is a great climax, suddenly subsiding, followed by a passage which will perhaps convey the impression of immense waves slowly gathering force until they smash themselves upon the impregnable rocks.

The theme of the sea is heard again, and the piece ends as it began, with a picture of the castle still proudly fronting the sun and wind of centuries.'

There is no unequivocal proof that King Arthur or any of the other shadowy figures mentioned in Bax's note had any connection with Tintagel. (The name comes from the words din and tagell, meaning 'fortress' and 'constriction' in the Cornish language, and refers to the narrow ridge leading to the castle ruins from the nearby village of Trevena.) Nevertheless, standing on the cliff-top there, with the magnificent fury of the Atlantic rollers battering the rocks far below, one can readily appreciate how the legends and the scenic grandeur must have fired Bax's imagination into producing some of the most vivid sea music ever written.