Through history, keeping time has been important, dating back as far as primitive man. Originally, the passage of time may have been measured by the transition from day to night, the tracking of stars, and seasonal changes. As mankind became more advanced, roughly 6,000 years ago, the desire for more accurate methods of time keeping arose. This came from the need to keep accurate time for things such as religious ceremonies, farming, or even bureaucratic gatherings. One of the first methods of keeping time began with sun clocks in Egypt. This was problematic, however, because it could not measure time in the dark or during days when the sun was not present. The failings of the sun clock made way for water clocks.
In order to be categorized as a clock, any device must satisfy certain basic requirements. The first of these requirements is to repeatedly mark time in equal amounts. The second requirement is that it must both keep track and display the passage of time. This was something that water clocks were able to effectively do.
Experts believe that the earliest water-clock was buried in 1500 B.C. in the tomb of Amenhotep I. Around 325 B.C. Greeks began using water clocks to keep time. They called them clepsydras, which meant water thief. These water clocks were vessels, or containers, that sloped at the sides and had a small hole close to the bottom. Water dripped from this hole steadily and constantly. Bowl, or cylinder shaped vessels were marked on the inside so that the passage of time could be measured. The water dripped steadily into this bowl-shaped vessel. The passage of time was marked by a float in the water that rose to meet the markings, which represented hours, within the bowl. This was not the only version of the clepsydras. Another version used metal bowls that were placed in larger containers of water. The metal bowl would have a small hole in the bottom, which caused it to gradually sink. The sinking would take place over a specific time period, which was used to measure the passing of time. These early water clocks, or clepsydras, were typically not the most accurate.
Over time, both Greek and Romans began to develop more sophisticated and advanced water clocks. These differed from the earlier water clocks that relied on water dripping from bowls, in that they were mechanized. Created by astronomers and horologists, not only were these clocks designed to regulate the flow and pressure of the water, but they were more elaborate in both design and their displays. Features of these early mechanized clocks included figures behind doors that opened, bells, and other movable parts such as pointers. The creation of these water clocks occurred from 100 B.C. to 500 A.D.
Around the 1st century, a Greek astronomer by the name of Andronikos built an octagonal clock tower in Athens. This tower included not only a water-clock, but also sundials and a wind vane. The structure stood 42 feet high and is called the Tower of the Winds. Each of the eight sides of the tower matched a point on a compass. Each of the sides was also adorned with figures of wind deities that represent the winds blowing from the direction that they faced. This is where the name Tower of Winds, originates. The Tower's clepsydra was mechanized and operated 24 hours, recording the time when the sun clocks were unable to do so. People who observed the tower could also see mechanical indicators for the hour.
From 200 to 1300 A.D., China began to create astronomical and astrological mechanized clepsydras. One of the most impressive of these water clocks was built in 1088 by Su Sung. The Emperor of China gave Su Sung this task, because he desired the best and most magnificent water-clock. When completed, the clock was nearly 40 feet high, and used a water escapement mechanism that had been created around 725 A.D. Su Sung's clock was able to not only power elaborate displays, such as rotating globes and figures ringing bells, but it was also able to keep relatively accurate time for a water-clock of that time. The clock was stolen in 1126.