Donaueschingen Festival
Metastaseis (; spelled "Metastasis" in correct French transliteration, or in some early writings by the composer "Métastassis") is an orchestral work for 61 musicians by Iannis Xenakis. His first major work, it was written in 1953–54 after his studies with Olivier Messiaen and is about 8 minutes in length. The work was premiered at the 1955 Donaueschingen Festival with Hans Rosbaud conducting. This work was originally a part of a Xenakis trilogy titled "Anastenaria" (together with "Procession aux eaux claires" and "Sacrifice") but was detached by Xenakis for separate performance.