The Sumerians of Mesopotamia, who is thought to have invented writing in the 4th century BC, based their numerical system on powers of 60 (instead of 100) subdivided into multiples of 10. It was from this system that Sumero-Babylonians developed the time system that we use today: each hour divided into 60 minutes, which are divided into 60 seconds.
In olden days time was told mostly by sundials and the first mechanical clock is thought to have been designed by an Italian monk around 1275. The clock was driven by the slow pull of a falling weight, basically like a very big hour hand.
Dating from about 1386, Salisbury Cathedral Clock is claimed to be the oldest working clock in the world. Like all clocks of that time it has no face but strikes the hour on a bell.
Today, the International Atomic Time, kept by 300 atomic clocks around the world, keeps earth’s time to within microseconds of accuracy of solar time. However, since the rotation of earth is slightly irregular and slowing down slowly, a leap second has to be added occasionally, giving us the world standard time known as Coordinated Universal Time (UTC).
If all of the above article gave you panic or anxiety, you probably suffer from chronophobia, the phobia of time!