It is notable for its use of the sixxen, an instrument Xenakis constructed specifically for the piece.
The title of this work is intentionally ambiguous: on one hand, the term comes from a word meaning "many", and which alludes to all of the instruments used by the six percussionists along the four movements; on the other hand, it refers to a myth in Greek mythology: the Pleiades are the seven daughters of Pleione and Atlas even though the greatest part of his inspiration may come from the astronomy, as the Pleiades were thought to be the stars from Taurus.
In Métaux (French, "Metals"), all of the six instrumentalists play an instrument called sixxen (a blend between "six", named after the six musicians, and "xen", named after Xenakis),[5] which is an instrument Xenakis had constructed specifically for this composition (they were made by the ensemble).
[6] The instrument in question consists of nineteen bars, of aluminum[6] or bronze and steel,[5] tuned microtonally (to an unequal 21-note scale built from 1/4 and 1/3 tones),[7] laid out keyboard-style, and it is meant to be played with metal hammers.
In Claviers (French: "Keyboards"), Xenakis uses vibraphones, marimbas, xylophones, and xylorimbas.