Ἡ Ύδραυλις εἶναι ἓνα μουσικὸ ὂργανο, ποὺ τὸ ἐφεῦρε ὁ μηχανικὸς Κτησίβιος στὴν Ἀλεξάνδρεια τὸν 3ο αἰῶνα π.Χ.
Ἡ ‘Υδραυλις τοῦ Δίου χρονολογεῖται στὸν 1ο αἰ. π.Χ. καὶ εἶναι τὸ παλαιότερο μουσικὸ ὂργανο τοῦ τύπου αὐτοῦ, ἀπὸ τὸ ὁποῖο προῆλθε τὸ ἐκκλησιαστικὸ ὂργανο τῆς Δύσης . 
Αὐτὸ τὸ ὂργανο παίζεται μὲ δύο ἂτομα . Ὁ ἓνας πατᾶ τὰ πλῆκτρα ἐνῶ ὁ ἂλλος πιέζει τὸν ἀέρα μὲ τὸ νερό. Ὑπάρχουν 24 αὐλοὶ καὶ 24 πλῆκτρα σὲ αὐτὸ τὸ ὂργανο…

A hydraulis is an early type of pipe organ that operated by converting the dynamic energy of water (Ancient Greek: ὕδωρ hýdōr) into air pressure to drive the pipes (Ancient Greek: αὐλός aulos). Hence its name hydraulis, literally «water (driven) pipe (instrument).» 
It is attributed to the Hellenistic scientist Ctesibius of Alexandria, an engineer of the 3rd century BC. The hydraulis was the world’s first keyboard instrument and was, in fact, the predecessor of the modern church organ.

1st century BC, Archaeological Museum of Dion, Pieria, Central Macedonia, Greece.

Φωτογραφία http://users.sch.gr/KAPEAPO1/ydraylis.htm