The earliest forms of time keeping were thought to be devised mainly for the use of astronomers. In ancient times much of mans knowledge and activities were determined and tracked by heavenly bodies. Because of this some form of time keeping became necessary. Certainly they had no use at the time for the watches we now so casually wear on our wrists that calculate time in milliseconds and are calibrated by radio signals from a far away atomic time clock.
No they were happy with any device that could just give them some standard measurement on a semi regular basis. Modern timepieces and actually timepieces dating back hundreds of years are possible because some form of controlled constant movement is available. Early devices used weights pulled by gravity to transmit energy to revolving cogs, gears and wheels to provide time as long as someone remembered to reset the weights. Pendulums were another early driving force. More advanced time pieces were made possible by the invention of coil springs which could keep pressure on the clock or watch movement and keep everything moving in synch.
Before technology had improved enough to introduce gears, springs, weights and pendulums some simpler method of movement was needed. Somewhere along the line, probably in Egypt, someone noticed that the sun caused shadows as the earth moved through it’s orbit. First obelisks were erected which allowed them to divide their day into morning and afternoon. Later more elaborate devices called sundials were constructed which enabled to keep what they thought was fairly precise time. Sundials could be large elaborate half spheres carved in stone or small pocket sized devices complete with a compass to align the dial and could be carried in a pocket. (Hmm. Were pockets invented yet I wonder?)
At any rate one could well imagine the joy they felt when these were first devised. It was not long though till a problem was discovered. Someone turned out the light. Yes, the sun went down. What to do? What other form of fairly accurate motion was known at that time? Flowing water.
Various forms of water clocks were devised. Some as simple as stone or metal bowls with calibrated lines inscribed inside. These containers had a small hole in the bottom which allowed a small flow of water to enter as the bowls were floated in a tub of water. Though crude they served a purpose. Later huge elaborate water clocks were built which used water movement to operate complicated mechanisms. These may have been efficient in Egypt where the weather was always warm or hot but in Northern climates the water tended to get hard as the temperature dropped which of course stopped the clock.
And you thought you had it tough because you have to remember to change the batteries in your kitchen clock once a year.