Gamelan is a traditional musical form originating in Indonesia. It is ensemble music that is based around groups comprised of predominantly metal percussion instruments, as well as the occasional flute, stringed instrument, or vocalist. The early origins of Gamelan are not clearly recognised however by the 12th century Gamelan music had an important role in court music. The Gamelan style was influenced by some other traditions, with the most notable change being the introduction of the gong which is now central to the musical style. The music is based around a central nuclear theme that is the core of the piece. Different instruments layer on top of each other playing embellished or altered versions of this nuclear theme in what is known as heterophony.