Plato and Aristotle focused on perfecting the polis (city-state), a tiny political entity, which for the Greeks meant both society and political system. The conquest of the Mediterranean world and beyond by Aristotle’s pupil Alexander the Great (336–323BC) and, after his death, the division of his empire among his generals brought large new political forms, in which society and political system came to be seen as separate entities. This shift required a new understanding of politics. Hellenistic thinkers, especially the Stoics, asserted the existence of a natural law that applied to all human beings equally; this idea became the foundation of Roman legalism and Christian notions of equality (see Stoicism). Thus, the Roman orator Marcus Tullius Cicero (106–43 BC), who was strongly influenced by the Stoics, was noteworthy for his belief that all human beings, regardless of their wealth or citizenship, possessed an equal moral worth.