Since time immemorial, there are clocks. Pretty much in all shapes and sizes - Wikipedia - lists about seventy. One of the oldest is the sundial, the youngest the atomic clock.
A clock measures time, shows the structure of the day, determines our schedule. Actually, that clock is a kind of tyrant, who says, now you have to get up, now you have to eat breakfast, now you have to go to school or to work, now you have to eat lunch, to go home, have dinner, do whatever.
Because the tyrant plays such an important role in our lives, we photograph him in all keys and angles; the clocks list proves it. Go and have a look and have a good time!