Hydraulos (Greek Hydraulos - water pipe) - it was an ancient Greek organ in which the air necessary for the game was compressed by the pressure of the water column. Invented was about 300-250 BC. Ketzibia
from Alexandria. Because of its loud sounds, it was readily used in the next centuries in the ancient pagan Greco-Roman world for the purpose of musical amusement.
This circumstance was the reason for the subsequent prohibition by the early Christian church of the game on the organ, as a sinful instrument. The description of the hydraulos was given by Geron of Alexandria (2nd century). The hydraulos keyboard had 19 keys. He had a scale, which allowed the use of Hyperlidian, Hyperasian, Lydian, Phrygian, hypolithic and hypophygian frets. This scale was invented in the 4th century. The pneumatic organ began to displace the hydraulos from use, and it disappeared in Western Europe as early as the 6th century finally.