Hydraulis, Hydraulikon

This is a pipe organ.


Organ console at the United States Naval Academy chapel

Without it we would not have this:

Or this:

Or this:

An entire era of films would have been almost unwatchable without organ music.

Centuries of music have been influenced by the distinct sound of organ pipes. But where did the idea come from and why? Who invented it? The organ and its descendants have been around for so long it’s difficult to imagine anyone actually inventing one.

Surprisingly (or not?), the story of the pipe organ begins way back in the 3rd century BC with the invention of the hydraulis.

In order for a set of pipes to be considered an “organ” it must have four elements:

1. Pipes, of course
2. A chamber that stores wind
3. Mechanically-generated pressure that sends the wind through the pipes
4. Sound/pitch/tones (what have you) must be controlled by some type of keyboard

The first historically recognized instrument to have all of those components was the hydraulis, also known as the hydraulikon. In plainer terms: a water organ. Consequently, the hydraulis is also the first known keyboard instrument!

Hydraulis Musices

Once upon a  time a Greek engineer named Ktesibios (or Ctesibius in Latin) was working in Alexandria, Egypt. This was during the 3rd century BC when the Roman Empire ruled the region. He was an incredibly gifted physicist and engineer and was known for his work with compressed air, a very new concept at the time. His father was a barber, which has been said to have inspired his first invention: a counter-weighted mirror that could be adjusted to the height of each client. He later invented forced air pumps, air-powered catapults and the water clock (clepsydra), among other things.

At some point it became worth his time to figure out how to enable one person to play a big set of pipes without having to blow air through them one at a time. People before him had tried to create a mechanized system to blow air through pan pipes, but those attempts had never amounted to much. Accounts suggest Ctesibius never set out to invent a new instrument, he just wanted to solve an engineering problem.


The hydraulis was an instant hit with the Greeks and Romans and made a huge impact in the musical world that would be felt for centuries. This engineering marvel inspired a sequence of mechanical improvements during the Roman era that ultimately led to the creation of the bellows system. It would take over 1,000 more years for the water organ to morph into the powerful and mechanically-complex instruments used in many churches today.

So how did it work?

A large set of pipes were placed on top of a case holding air pumped through valves. Between the pumps was a water tank that regulated air pressure within a funnel-shaped air tube inside the case.


Image by Kostas Kotsanas

Levers on the side of the hydraulis were used to manually pump air through the air supply pipes. Each pump had a non-return valve that was checked by bronze dolphins so air wouldn’t be sucked back out when the weight dropped. To keep the air pressure constant inside the case, excess air could escape through a small opening at the bottom of the inverted cone-shaped funnel in the water tank. With a constant moving air supply inside the case thanks to the pumps, the pressure (kept in check by the weight of the water displaced by the air pumped through the funnel) would force air through the air supply tubes leading to the pipes without breaks in the sound. A keyboard with 19-24 keys controlled air flow through sliders or small valves. When the key was pressed, air would escape through the pipe associated with it, creating a unique tone. The larger the pipe, the deeper the tone.

The result was something like this:

Ctesibius’ work and his original design  might not have survived had it not been for the writings of Hero of Alexandria, Philo of Byzantium and Vitruvius, famous writers and engineers back in the day. The popularity and regular use of the hydraulis in Roman society was well documented in art and various writings, but only Hero and Vitruvius described its actual components in technical detail. Vitruvius even added some of his own flair to the original design. Different designs for similar water organs were later developed, including one that was powered by a windmill.

We know through many sources it was used as a solo instrument and often accompanied games and festivals. An organ competition was held in Dion in 90 BC (someone named Antipatros won). Anybody who was anybody got to play on the hydraulis. Bigwigs like Cicero compared organ music to the finest food and, um, physical pleasure. Nero himself promised to play in the Circus if he beat the Gaul.


The hydraulis remained a major part of Roman life until around 500 AD when the Empire fell apart. It is documented that the Byzantine Empire (founded in 330 AD) and the Arabs also used the hydraulis, each developing their own versions of the water organ based on the late Roman adaptation that replaced the original hand pumps with bellows. It’s unclear whether the water tank was replaced too at this point. Some other method of air pressure would have had to be developed to replace the weight created by the water level rising and falling. Nobody really knows for sure when the water tank component was eliminated.

After the fall of the Roman Empire, Western Europe lost a huge amount of Roman knowledge, including the organ. At least until Constantius, Emperor of Byzantium, gifted one to Pepin the Short, king of the Franks in 757. Monks were quickly put to work to try to re-create the organ and teach organ building to students. By 900 the organ had found a permanent place in churches and the rest is history!

A little note about stops before you go

It is worth mentioning that in some ways the Roman hydraulis was actually superior to the medieval church organs that existed prior the the 15th century. Ctesibius’ and Vitruvius’ prototypes incorporated stops that enabled the organ to access multiple registers, meaning its musical range was much wider. If you don’t know what an organ stop is, keep reading.

Stops are components that control which set of pipes the air blows through. Many organs have multiple sets of pipes (ranks) that change the octave or type of sound the notes make. Modern organ stops look like buttons or knobs.


The Roman hydraulis had two or three registers controlled by stops, which gave the instrument a much wider and richer musical range than it would have with one set of pipes alone. Medieval organs, however, also had multiple ranks of pipes but had not yet incorporated a stop system to control which set the air would blow through. The result was multiple pipes going off at once and the musical range being limited to the number of keys on the keyboard, which wasn’t many. On a medieval organ with multiple pipe ranks each note might play 2–3 different octaves at the same time!

The hydraulis truly was a unique and marvelous instrument and the quality of its sound remained unmatched for centuries. Thanks to Ctesibius’ genius back in 270-ish BC we can now part ways with this gem: