on policing the city

... Just as they lead colts to noises and confusions and observe if they're fearful, so these men when they are young must be brought to terrors and then cast in turn unto pleasures, testing them far more than gold in fire. If a man appears hard to bewitch and graceful in everything, a good guardian of himself and the music he was learning, proving himself to possess rhythm and harmony on all these occasions- such a man would certainly be most useful to himself and the city. And the one who on each occasion, among the children and youths and among men, is tested and comes through untainted, must be appointed ruler of the city and guardian; and he must be given honors, both while living and in burial and the other memorials. And the man who's not of this sort must be rejected."

Plato's Republic (414e)