Bartók's Music for Strings, Percussion and Celesta was written in 1936, commissioned by Paul Sacher, founder and conductor of the Basle Chamber Orchestra, whose patronage has been so important in music of the twentieth century. It was first performed by the orchestra under its conductor in Basle on 21 January 1937. The work is scored for two groups of strings arranged on either side of percussion instruments that include side-drum, snare-drum, cymbals, tam-tam, bass drum, timpani and xylophone, with celesta, harp and piano. The first of the four movements is opened by muted violas with a slow chromatic melody, imitated by the violins on the right of the conductor and then by both groups of cellos, followed by an upper violin part. Each entry is on alternate upper or lower notes of the circle of fifths, a further example of the meticulous symmetry of the work that has led to plausible theories of mathematical analysis, for which there seems considerable justification. Here the successive entries lead to a central entry on E flat, the climax of the movement, after which the process is reversed. The second movement, thematically related to the seminal first movement theme, contrasts the two string groups in its opening and is broadly in sonata form, with exposition, development and final recapitulation. The Adagio, another example of the composer's night-music mood, opens with xylophone and timpani, joined by tremolo cellos and double basses, through the sound of which the first viola melody emerges. The movement is constructed sectionally, each of the six sections in complex relationship with each other and with the motifs that make up the opening theme of the whole work. The final movement, in form essentially a rondo, introduced by two clear notes from the timpani, continues with a pattern of pizzicato string chords, arpeggiated downwards, against which the second group of strings introduce a Bulgarian folk-dance rhythm with a melody derived from the opening theme, here presented in ternary form. The movement ends stridently enough, reaching a final consonant A major chord.