Augustine’s question: what is the difference between a kingdom and a band of robbers? identifies that law cannot be understood as a social institution without considering its relationship to justice. That relationship is complex because despite law’s necessary reference to justice, the justice which is achievable is only ever approximate, and law’s use of rules makes it impossible for laws to do justice in all individual cases. Rulers claim that their rule is just: that the law is made by those who have the right to make it, that it is substantively just, and that law will be obeyed by all to whom it applies. Through the key claim that the laws are just, rulers seek to induce voluntary obedience and to justify the use of force when obedience is not volunteered. Augustine was clear-eyed about such claims, stressing that the Pax Romana was victor’s justice.