The making of Mahler's Tenth Symphony

Mahler's Tenth Symphony is one of the most troubling, paradoxical works in musical history. Unfinished at his death, its composition formed part of a legendary, if futile, attempt to ward off mortality. While working on the score, Mahler also underwent a profound personal crisis that led him to consult Freud. The Tenth is consequently the ultimate musical act of agonised self-revelation - though its psychoanalytic intimacy can only be approached through one or more of its completions, none of which may be an accurate reflection of Mahler's final intentions.

Most of the tales surrounding the Tenth derive from the testimony of Mahler's narcissistic wife Alma and, in particular, her unreliable memoirs of her life as companion to a succession of famous men, of whom Mahler was the first. It is to Alma that we owe the idea that Mahler had an unconscious gift of prophecy and that his music was riddled with arcane premonitions of catastrophe. Writing with hindsight, Alma saw his song cycle, Kindertotenlieder, completed in 1904, as a portent of the death of their daughter Maria three years later. She also elevated to the level of myth the idea that his last works constituted an attempt to, as she put it, "give God the slip".

Shortly after Maria's death, Mahler was diagnosed with a potentially fatal heart condition. Superstitious, he fretted about the significance of symphonic numerology. Beethoven died after writing his Ninth; Bruckner died while writing his. Mahler had just completed his Eighth. Death could perhaps be cheated, if his next symphony was named rather than numbered - Das Lied von der Erde. "When he was writing his next symphony, which he called the Ninth," Alma writes, "he said to me, 'Actually, of course it's the Tenth.' Finally when he was composing the Tenth, he said, 'Now the danger is past.' Yet he did not live to see the Ninth performed, or to finish the Tenth."

Alma over-emphasised this tale to deflect from her more worrying, albeit defining, role in the Tenth's history. In the summer of 1910, just as Mahler had completed the sketches for the first two movements, he discovered Alma was having an affair with the architect Walter Gropius, later her second husband, whom she met at a sanatorium while being treated for depression.

Mahler's marriage had, in fact, been troubled from the start. Alma was herself a composer of some talent, though not a genius. Mahler, however, demanded she give up her own creativity to serve his. In later relationships, this was a role she was willing to play, though with Mahler she felt stifled. After Maria's death, Mahler also needed solitude in which to grieve. Alma desperately wanted company and support. The memory of the child gradually became a wedge between them.

Mahler, it would seem, found out about the affair when a letter, sent by Gropius to Alma but wrongly addressed to Mahler, arrived at Toblach, the country retreat where he spent the summer composing. Gropius soon pitched up in person, and if Alma's accounts are to be believed, there was a three-way confrontation, during which Mahler, clutching a Bible, said to her, "Whatever you do, will be well done. Choose!" She ostensibly elected to stay with her husband. "Gustav's love is so boundless that my remaining with him means life to him," Alma told Gropius, whom she continued to see without Mahler's knowledge, a fact she withholds in her memoirs.

Both Alma and the distraught Mahler, significantly, placed the responsibility for their marital breakdown on his neglect, and his agony was soon such that he decided, possibly at Alma's prompting, to consult Freud, making a 24-hour journey from Toblach to Leiden, in the Netherlands, where Freud was on holiday. The only surviving documents surrounding their meeting derive from Freud's discussions, years after the event, with his pupil Marie Bonaparte. Freud argued that both Mahler and Alma had sought a relationship with a partner modelled on an idealised image of the parent of the opposite sex. His conclusions now strike us as predictable, and many have turned for a more accurate indication of Mahler's mental state to the manuscripts of the Tenth, which Alma edited for publication a decade after his death.

The last three movements are annotated with what Alma, astonishingly, called "these outcries and ejaculations addressed to me". Mahler's language is essentially that of martyrdom. The brief, crucial central movement, Purgatorio, is accompanied by the Christ-like superscription: "Oh God, why hast thou forsaken me!" At one point he pleads for annihilation, "that I may forget that I am", though at the end self-laceration gives way to calm. The final pages are annotated with, "To live for you! To die for you!" with the single word "Almschi" under the closing bars.

Before his death, Mahler finished the orchestration of the opening Adagio, which was first performed as a fragment in 1924. Alma was ambivalent, however, as to whether she would permit the symphony to be completed, eventually offering the task to Schoenberg, who turned it down. She initially objected to Deryck Cooke's now familiar version, only permitting a performance of extracts as a "lecture demonstration" in 1960, though in 1963, two years before her death, she withdrew her ban. Since then, completions of the Tenth have proliferated, though Cooke's revised edition, first heard in 1972, is most frequently used in performance. Even here, controversy won't die down. Many conductors have refused to perform the completed score.

This is regrettable, for Mahler's Tenth, in any version, is a great work, traversing an unremitting arc of emotion, at times almost unendurable in intensity. At various points, the music becomes entangled in an unforgettable, reiterated nine-note dissonance - associated perhaps with the fatal nine symphonies - from which it then struggles free. The Purgatorio section derives from an earlier song dealing with infant mortality - Mahler's cryptic acknowledgement, perhaps, of the effect Maria's death had on his marriage. Purgatorio, however, also implies blessedness after turmoil, and the symphony's closing bars convey an atmosphere of genuine serenity, unique in his turbulent output. One is tempted to conclude that in composing them, Mahler had overcome his dread of death and his love for his errant wife was, indeed, as "boundless" as she claimed.

· Mahler's Tenth is at the Barbican, London EC2, on Wednesday. Box office: 020-7638 8891.