This performance was flagged at the time as the ‘Tristan of the Century’, a claim in the event not too exaggerated. Musically and, for much of the time, dramatically, this rendering is arresting in all its aspects. It is imaginatively filmed by Pierre Jourdan and staged by Nikolaus Lehnhoff in the vast Roman amphitheatre at Orange. Heinz Mack, who provided the astonishing scenic and lighting interpretation, also deserves a mention. Huge pieces of white canvas surround a white platform on which the sole props are two small staircases, altered to suit the needs of each act’s milieu. Huge spotlights enhance and counterpoint the action. It is a bold setting suited both to the venue and to the work, showing that simple, timeless methods (derived from Wieland Wagner’s approach to his grand-father’s work), can mean so much more than mere ‘concepts’. It closes in a moving Liebestod of divine transfiguration.

That also proves the climax of Birgit Nilsson’s unforgettable Isolde. By 1973 she was already 55 but you would hardly have known it from the amazing concentration, stamina and, above all, beauty of her singing, enhanced by her accomplishment in every aspect of the heroine’s character (and hardly bothered by the prevailing mistral). She is marvellous, as ever, in the bitter irony of Act 1, soft-grained in the love duet, serenely elevated in Act 3. We shall not hear her like again. Beside her bestrides the big (in every sense) Tristan of Jon Vickers. He performs the role in a way that suited him but one that would not be advisable to imitate. In good form, he sings with breadth of tone and phrase, marred only occasionally by his tendency to sing in a kind of enhanced Sprechgesang, and offers a singular intensity of tone and acting hard to describe. His account of Tristan’s Third Act hallucinations is as frighteningly real on screen as it was in the theatre. Nilsson named him her favourite Tristan, and one can realise why when he is so involved and involving.

Ruth Hesse sings an ample-sounding Brangäne of a kind hardly heard today, and interprets the part with apt sympathy. Bengt Rundgren’s Marke is huge in voice and carriage; he sings his monologue as an exercise in bel canto while catching all the man’s inner torment. Walter Berry’s soundly sung Kurwenal is a little disappointing, his baritone surely a size too small for this vast space.

Over all presides the 78-year-old Böhm, master of every emotion and nuance in the score, realising all its poignancy and complexity; and persuading the French Radio orchestra to great things, although his Bayreuth audio-only recording is still better. The major drawback to the issue is that the orchestra is too distant and its sound partly occluded, a fact some intending buyers may baulk at. My ear soon adjusted to what was and is a serious attempt to match image to music, an experience not to be missed.