Archaeological Museum of Dion:

The hydraulis of Dion, a sophisticated musical instrument, precursor to the western pipe organ. The Dion hydraulis is the oldest such musical instrument found (1st century AD). Detail: a small glass plaque in the millefiori technique from the decoration of the organ.

Clay models, and depictions on mosaics of the instrument have also been found:  (terracotta model found in Tunisia now at the British Museum, mosaic from Villa Nennig, Germany)