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Understanding The Clepsydra


It is an almost innate human need to count our seconds, to track time. Our ancestors had devised many clever ways to tell time; everything from the reading of the stars in the heavens, to the passing of shadows across stone. Today, we will be focusing on one particular method of time keeping that is simple in concept, but whose utility and potential would far outstrip its contemporaries. And though this method would arise in multiple places at various points in time, such as China, India, Babylon, and Egypt, we will focus on the Hellenistic world and its successors; today we shall explore the fascinating Greek Water Clock. 

An Ancient Water Clock

Often referred to as a “Clepsydra” or “Water Thief” these ingenious clocks would use the flow of water to measure time. Some of the earliest designs were as simple as two buckets, one placed above the other. The higher one would have a small hole in the bottom lip of it and would allow water to stream out and into the lower one at a relatively consistent rate. As the water level rises in the bottom bucket, it passes small lines or markings on the inside bowl of the bucket that were used to denote a series of set increments of time. Fundamentally, all a Clepsydra would need to function were water and gravity. Thus making it an incredibly reliable time keeping device, not affected by such things as clouds or night, it was a natural improvement over the sundial. This design was not without flaws however, and required a constant eye to ensure it would keep proper time. As water levels lowered in the top bucket, the outflow rate would slow and it would take longer to drain and fill the bottom bucket. This problem was handled by having someone watch the Clepsydra to empty the bottom bucket and refill the top to ensure that the waterflow was consistent.

Such water clocks would see widespread, and varied use throughout antiquity. In the city of Athens for instance, Clepsydra were used to fulfill all manner of time keeping needs. They were used in the innovative Athenian courts to measure the amount of speaking time allotted to each speaker in a given case. This was used to ensure that both defendants and prosecutors would have an equal say in the court. The court system in Athens was sacred, with the truth and fairness being paramount. In this capacity the use of the Clepsydra was ritualized and almost sacred in itself due to its part in ensuring the impartiality of the Athenian Justice system. These courts were a fundamental part of Democracy and the society of Athens; both the Athenian system, and its courts would go on to influence American Courts and Democracy. On the less savory end they were also used to time the length of a patron’s stay at a “house of ill repute”, whereupon he would be charged a certain amount depending on how much time they had spent in their services.

As time progressed and technology improved, so too would the design of the Clepsydra. There would be many Greek and later Roman Astrologers and Horologists who would refine this simple yet innovative device, forever striving for more accuracy in timekeeping. One figure however stands apart from the rest, the Third Century BCE Alexandrian Inventor, Ctesibius. Born in 285 BCE, little is known of the man himself, but what is known paints a picture of a remarkable man with an astounding intellect. We know his first career was not as an inventor but rather a humble barber. One of his first inventions was actually a counterweighted mirror designed to assist him when he was performing haircuts. He would later go on to become the first Head of the Museum of Alexandria, a position that would allow him to further his experiments and go on to invent some remarkable devices. He had a fascination with water, counterweights, and siphons, and would use all three to invent the first Water Organ, which his wife was apparently quite good at playing. This organ would later go on to inspire the church organs commonly found in Christian churches. But his most impressive innovation were his improvements upon the Clepsydra. At the time, Alexandria was a city renowned for its knowledge and learning, particularly in the many fields of science. One of the city’s most important and widely sought after expertise was the study of medicine and health. The Medical field would benefit greatly from Ctesibius, who would invent an entirely self regulatory version of the Clepsydra that required no outside intervention. Since your more traditional Clepsydra would require someone to watch the lower bucket to empty it when it fills up to restart the clock, it functioned more akin to a timer or a stopwatch than our more modern notions of a timekeeping clock. Thus, limiting the practical application of the Water Clock. But this new design would use an ingenious three tiered system that would regulate the flow of the water so that it no longer required constant refilling and emptying to keep the water flow consistent, it also used a float and pointer system,
operating as a rudimentary hand, to indicate the passage of time instead of the water level. This incredible advancement would be used to great effect by not only the courts but also Alexandria’s renowned physicians, who would use the new design to track heartbeats and notate any irregularities like arrhythmia and heart disease. Ctesibius’s improved water clock would remain the most accurate timekeeping device until the invention of the pendulum clock by the Dutch Physicist Christiaan Huygens in 1656 CE, some two thousand years later.

Never ones to be satisfied with what they had, the Romans would later develop their own ingenious Clepsydra used for tracking the very movement of the heavens themselves. One such stellar clock was found in an Archeological site called Vindolanda, along Hadrian’s wall in modern day England, UK. This Roman clock functioned on similar principles to the three-tiered Ctesibius model, but on a larger scale. It had a massive upper tank that would fill up a second regulatory tank that would control the flow of water into the third, which had a float inside it. This float was attached to an axel and counterweight via a rope, and as the float would raise with the water level, the rope turned the axel which in turn rotated a massive bronze disc. This bronze disc was the actual face of the clock as we would know it and featured a map of the stars centered on the north pole. As the dial turned, a series of holes along the edge would be plugged, these represented the sun passing through a particular part of the sky and thus marked the day had passed.

The whole process of turning the dial took 24 hours and was used to track the days and the constellations as the year progressed. Astronomy and dates were very important to the Roman people, as they were deeply superstitions and would often use the stars to predict outcomes of certain events or tell prophecies, it was also important to know the date so that certain religious festivals and sacred rites such as Lupercalia and Sanguinala would be observed and carried out at the appropriate time.

With this in mind, it is easy to see how and why the Romans would spend the energy and resources necessary to build such massive time keeping contractions even in the far flung reaches of the empire such as the one found in Vindolanda.

Simple in concept, but brilliant in its many executions, the Water Clock, or Clepsydra of Mid to Late Antiquity was a fascinating step along mankind’s path to the mastery and understanding of time. Originating as little more than a system of buckets, it would evolve into precise self-regulated clocks used in medical procedures, and later still into immense stellar calendars on the border of civilization. The sheer variety and widespread use of this technology is a testament not only to the utility that a Clepsydra had but also to that uniquely human need, the need to count the seconds of our lives, and track the passage of time.