The Roman frame: orator, consul, philosopher; the De Republica, De Legibus, De Officiis; his career (and murder) spanning the republic's death-agony — the thinker of civic virtue againstdictatorship.
The res publica: the commonwealth is the people's affair (res populi) — a people united by agreement on justice and common interest; the state a moral partnership, not a property. Civic duty (the officium of De Officiis — through Pufendorf into modern constitutional ethics) binds citizen and statesman alike.
The concept of law (the natural-law doctrine — Jurisprudence Unit 3.1's Romanchapter):
1. True law is right reason in agreement with nature — universal, unchangeable, everlasting; it cannot be repealed by senate or people; it "summons to duty by its commands… and thwarts the wicked." There is one law, eternal and unchangeable, for all nations andall times — one master and ruler, God.
2. Human law's validity derives from this: statutes that conflict with natural law are not binding — "the wicked command of a tyrant" is no law; corruption of custom does not corrupt the measure.
3. Law's unity with justice: law is "the distinction between just and unjust," the bond of the commonwealth — an unjust "law" names nothing (De Legibus' argument — the lex injusta tradition's fountainhead). The statesman: Scipio's Dream (De Republica's close) — the ruler's true glory is the citizen's safety; government's forms are instruments; the mixed constitution (Rome's own: consuls/senate/tribunes) recommended against the six-fold's instabilities — the model Montesquieu would copy. Legacy for law: natural law enters jurisprudence through Cicero (the Stoics' pupil, Aquinas's quarry); "right reason" becomes the international law of Grotius; and every constitutional court striking down "unjust" statute speaks, knowingly or not, his sentence.