It is traditionally considered that the ideas relevant to the concept of Natural Law were for the first time articulated in the polemic of Socrates/Plato against the sophistic doctrine of Conventional Law. But Plato was engaged in arguments not only with the Sophists - he also struggled against indefinite, in many respects antinomic, unreflective ideas of law expressed by average Athenians whereby Law and Power, Law and Status were confused. Plato's appeal to the mythological narrative in the places where he discusses the theme of Natural Law makes it clear that even to his mind the concept of Universal Legislation shows its heterogeneous and problematic character. We argue that Carneades' opposition of Natural and Positive Laws owes precisely to this problem. Cicero inherited this strategy and made it even more radical. His preaching of the idea of natural Law (in its Stoic version) becomes in his texts rhetorical topos, which was well known to the readers. Nevertheless Cicero expresses doubts about that simple scheme according to which Positive Law appears a specific representation of Natural Law and tries to trace particular causes, which motivated the concrete forms of positive Law.