Timekeeping developed in early recorded history, with different societies using their natural surroundings and devices they created to help keep track of time
. The basic units we use to keep time have not evolved greatly, showing their ancient historical roots. The keeping of time was important to early agriculture, particularly in irrigation where timing access to water was important. Increasingly, timekeeping was not just conducted by the select few by much of society.
==Early Timekeeping Devices==
Some of the earliest timekeeping devices involved the use of water, or what were called water clocks or <i>clepsydrae</i> as called by the Greeks. This involved either using outflow of water or inflow. Effectively, as water drained out or filled in, the rate was seen as relatively constant based on marking on containers would then tell how much time had passed as the water drained or filled in. Such devices were known to have existed in many of the earliest complex society in Eurasia, including in Egypt, Mesopotamia, the Indus, China, and likely other regions, including ancient Greece and Rome. In China during the Han dynasty, water clocks were critical for astronomical observations and became an increasingly complex set of tanks that also had secondary tanks that would provide additional water to keep water moving to measure time as pressure changes could mean that the rate of which water moved changed, thus potentially invalidating any time measure.
Other early devices include candle clocks, which were probably only used indoors. These were also throughout much of Eurasia from the Bronze Age and throughout the Medieval period. Candle clocks were simple, where the rate of burning would be constant and the candle would be pre-measured so that different levels in which the candle melted as it burned would help tell time. The sundial is likely another ancient device. Both the Babylonians and Egyptians used the sundial at least by the 2nd millennium BCE if not earlier
. The sexagesima system we use in our own clocks today was already used and invented by the Sumerians and Babylonians, which was also likely used for initial sundials. The oldest sundial appears to date from around 1500 BCE, but sundials are likely much older.
The Greek philosopher Philo in the 3rd century
BC and in China, under development by the mathematician Yi Xing by the 7th century, escapement clocks were built, which use a mechanical device that releases a gear which then allows the rate of release to be used as a timekeeping element. This is similar to our mechanical clocks and such clocks would begin to signal the increasing realization that mechanical timeclocks would be the only way to keep time more consistent.
Medieval period, clocks continued to use some of the older methods, such as sundials and water clocks, while also incorporating newer methods that included escapements. Other inventions by this time also included the hourglass, which was first known to have been used by the early Medieval period in the 8-9th centuries in Germany. The origins of the hourglass, however, could be much older. The key inventions were more sophisticated tower clocks that used more advanced water clocks and hydraulics, which would wind and use torque in mechanical component to tick at given intervals, such as every hour. Early examples include the Great Mosque in Damascus and the Mustansiriya school in Baghdad. One advance came in the early 13th century under Al-Jazari, who was an Islamic scholar who perhaps created one of the first fully automated clocks and even created a clock that would have programmable automata musicians that played for guests and could be reprogrammed. Some have described this as the earliest form of computer programming. Nevertheless, by the 13th century, mechanical clocks were becoming more common, although often still powered by water. Town squares throughout Europe were also putting up tower clocks as a way for townspeople to keep track of time and to be informed of important events such as time to prayers.