The First Gamelan
Among the earliest evidence of gamelan instruments is a series of stone relief carvings on the Borobudur Buddhist temple in central Java (ca. 800ad).
Borobudur shows the world's first record of a bar percussion instrument. It appears to be a gambang style "xylophone" with ten wide bars resting over a trough resonator. We have no way to tell, but the bars were most likely made of wood or metal. The instrument is shown being played with two sticks with large, presumably padded, balls on the ends (see Kunst, "Hindu Javanese Musical Instruments," fig. 21). Cymbals resembling Balinese ceng ceng kopyak used in modern processional music can be seen as well as two-headed hand drums which appear to be of both Javanese barrel shape and Balinese conical styles.
The reliefs of Borobudur and other central Javanese temples of the period, including Prambanan and Candi Sari, depict many other instruments including zithers, lutes, harps, vessel drums (gatam), and transverse flutes. Most are extinct in Indonesia today and may have never really existed on the islands, possibly carved from memory by mainland artisans. Only the bar instrument, cymbals, and drums remain. Notably absent from all reliefs of this period are gongs.