Marcus Tullius Cicero (c 106 BC – 43 BC) was a Roman philosopher, politician, lawyer, orator, political theorist, consul, and constitutionalist.
Cicero developed on Zeno’s school of Stoicism: Nature was synonymous with reason, reason was synonymous with god. Cicero said [natural law is] the highest reason whose natural function is to command right conduct and forbid wrongdoing.
Cicero believed that the natural law is accessible to everyone by reason alone. Cicero believed that real justice transcends human expediency, that such justice rests on the discovery of, and on the application of, objective principles that are universally applicable. Cicero was opposed to the notion of legal positivism and was aware of, and commented on, law that impugned on these rights (or universal truths) as ‘against the natural law’. Examples of this would be the right to self-defence, prohibition against cheating or harming others.