Cicero's famous book on duty was largely borrowed from a Greek Stoic
Cicero's On Duties shaped European ethics for centuries, but its first two books took their substance from a lost treatise by Panaetius of Rhodes. This Stoic softened his school's harsh doctrines into practical advice for ordinary people, and carried them to Rome under the protection of Scipio Aemilianus.
Born around 185 to 180 BC into a distinguished Rhodian family, Panaetius studied in Athens, attaching himself mainly to the Stoics Diogenes of Babylon and Antipater of Tarsus. Probably through Gaius Laelius he met Scipio Aemilianus and, like the historian Polybius, won his friendship. Both men joined Scipio's embassy to the kings and states of the Hellenistic east in 139 to 138 BC. In Rome he taught distinguished pupils and spread Greek philosophy. After Scipio died in 129 BC he divided his time between Athens and Rome, succeeded Antipater as head of the Stoic school, and turned down Athenian citizenship. His leading student was Posidonius.
He reshaped Stoicism into something more eclectic, so much so that later Neoplatonists counted him a Platonist. He dropped the doctrine that the universe periodically ends in fire, doubted divination, and ranked physics above logic. He rejected apatheia, the ideal of freedom from passion, accepted that some pleasant feelings accord with nature, and argued virtue alone is insufficient without health and adequate means. Moral rules, he insisted, should be usable by people who had not yet reached wisdom.
In politics he saw the city as a social contract formed to protect property, urged justice even towards slaves, and dismissed Plato's ideal republic as unrealistic. Following Polybius, he praised Rome's mix of monarchy, aristocracy and democracy, and went further in defending Roman conquest as a civilising duty that bound the victor to the vanquished. War he called inhuman, acceptable only as a declared last resort for defence or redress, with surrendered enemies treated decently.
His On Duties had three planned parts: what is honourable, what is useful, and how to settle apparent conflicts between them. He never wrote the third, and Cicero claimed to have completed it himself without leaning on Posidonius. Panaetius also wrote on cheerfulness, providence and philosophical schools, all now lost.
Source: Panaetius
