Commissioned by Ensemble intercontemporain for the ensemble’s tenth anniversary, the composition was premiered under Pierre Boulez on 26th January 1987. is approximately 15-minute-long piece is uniquely scored (similarly to Arnold Schoenberg’s Chamber Symphony) for 15 instruments which represent, in a miniature, the various colours of a large orchestra. 

There are five woodwinds, four brass, five solo strings, and a harp. Such a complement of musicians makes this composition stand out among Xenakis’s other works for unusual performing forces (for instance, Eonta for piano and five brass instruments of 1964 and A Colone for male choir, three horns, three trombones, three cellos, and three double basses of 1977), as well as his numerous pieces for homogeneous instrumental groups (e.g. Syrmons for 18 strings, 1959; Persephassa for six percussionists, 1969; Akrata for 16 woodwinds, 1965). Notably, this “miniature symphony orchestra” (including a traditional harp) lacks percussion, which Xenakis did employ in another similarly scored work from this period, alleïn, written in 1984 for the London Sinfonietta. Classical orchestral texture is, naturally, quite absent from Jalons, whose musical language and instrumentation are representative of Xenakis’s style. As is frequently the case in his music, the strings, for instance, are instructed to avoid any kind of vibrato. 

The piece consists of six sections performed attacca, employing six different tempi whose order is determined by the musical narrative. Section I is based on the formation and (sudden or gradual) disappearance of sound blocks linked by instrumental  “bridges,” later—on the overlap of strident glimpses of the woodwinds with gradually established string glissandi. Section II starts when the glissandi turn into microtonal oscillations. The opposition of instrumental groups suddenly gets resolved in a tremolo fortissimo of the whole ensemble. 

Section III, which can be interpreted as tripartite, has dense outermost parts oscillating between rhythmic synchrony and delay, surrounding a more polyphonic central segment whose lively melodic lines follow one another and converge. Section IV is characterised by explosive, broken-up outbursts of sound in the low register, above which rough clashes of high-pitched instruments can be heard. 

Section V opens with a veritable cloud of individual motion, which is gradually ordered and unified, leading to a return of the opposed instrumental blocks known from the previous movements. The sixth and last episode, restoring the initial tempo, starts fortissimo with a melody of timbres passed on from one low instrument to another. The other instruments promptly join this block texture, which is similar to that of the opening section. 

Jacques-Marie Lonchampt