Sp as you can be seen - watched

 control over people (power) can be achieved merely by observing them. 

So, for example, the tiered rows of seats in a stadium not only makes it easy for spectators to see but also for guards or security cameras to scan the audience. 

A perfect system of observation would allow one “guard” to see everything (a situation approximated, as we shall see, in Jeremy Bentham’s Panopticon). 

But since this is not usually possible, there is a need for “relays” of observers, hierarchically ordered, through whom observed data passes from lower to higher levels.