Opus clavicembalisticum is a work for solo piano composed by Kaikhosru Shapurji Sorabji, completed on 25 June 1930. It is notable for its length and difficulty: at the time of its completion it was the longest piano piece in existence. Its duration is around 4–4½ hours, depending on tempo. Several of Sorabji's later works, such as the Symphonic Variations for Piano (which last probably about nine hours) are even longer. At the time of its completion, it was possibly the most technically demanding solo piano work in existence due, for the most part, to its extreme length and rhythmic complexity and to the vast resources of physical and mental stamina demanded by its many passages of transcendental virtuosity, although some works conceived by New Complexity, modernist and avant-garde composers, along with Sorabji himself, were more difficult still; it is in this particular area that Opus clavicembalisticum primarily receives its notoriety, and to this day is still highly regarded in that light. Sorabji may in part have been inspired to compose the work after hearing a performance by Egon Petri of Busoni's Fantasia contrappuntistica and Opus clavicembalisticum to some degree embraces an homage to Busoni's work. Sorabji's earlier (1928) Toccata No. 1, also for piano solo and likewise a multi-movement work, evidences similar Busonian influence and is in some ways a precursor of Opus clavicembalisticum. Structure Opus clavicembalisticum has twelve movements, of hugely varying dimensions: from a brief cadenza, lasting only three minutes, to a mammoth interlude, containing a toccata, adagio, and passacaglia (with 81 variations), requiring around an hour to play. The work's movements are set in three parts, each larger than the last: The manuscript and publication both erroneously say that the sixth movement (Interludium primum) has forty-four variations instead of forty-nine. Composition and dedication In a letter upon completion of the massive work on 25 June 1930, Sorabji wrote to a friend of his: With a wracking head and literally my whole body shaking as with ague I write this and tell you I have just this afternoon early finished Clavicembalisticum... The closing 4 pages are so cataclysmic and catastrophic as anything I've ever done—the harmony bites like nitric acid—the counterpoint grinds like the mills of God... (underneath he quotes the last chord of the work, with "I am the Spirit that denies!") The dedication on the title page reads: "TO MY TWO FRIENDS (E DUOBUS UNUM) HUGH