The Republic is written by Plato around 380 BC and deals with the definition of justice, the properties of a just human being and a just state.
Plato explains his definition of a just man, through a dialogue held by Socrates among others, as a man fulfilling his appropriate role, and consequently giving to the city what is owed. That it is a man’s advantage to be just and disadvantage to be unjust and that one should look for justice in a city rather in an individual man.
“For it is likely that if a city of good men came to be, there would be a fight over not ruling, just as there is now over ruling; and there it would become manifest that a true ruler really does not naturally consider his own advantage but rather that of the one who is ruled.”
– Plato, The Republic of Plato