Zeno (c. 334–262 BCE) was born in Citium on Cyprus, probably the son of a merchant of Phoenician descent. The story has him shipwrecked into Athens, finding Xenophon's account of Socrates in a bookshop and asking, 'Where can I find such men?' He became a student of the Cynic Crates, drifted through several schools, and around 301 BCE began teaching beneath the painted colonnade in Athens's Agora — the *Stoa Poikile*. The school took its name from the place.

The Stoic system has three parts: logic, physics, ethics. Physically, the universe is a single living whole ordered by an immanent reason, *logos*; everything is part of that logos, and the human mind is a small spark of it. Ethics follows from this cosmology: the good life is *life according to nature*, i.e. according to logos. Happiness has nothing to do with pleasure or wealth; the only true good is *virtue*, the only true evil is *vice*. Health, money, reputation, the survival of one's family are 'preferred indifferents' — to be valued, but not the substance of a good life.

The most famous distinction is between what is *up to us* and what is not. Our body, reputation, what others think of us, natural disasters — none of these are fully in our power. Our judgements, intentions and reactions are fully in our power. The Stoic discipline turns all energy onto the second set and accepts the first with equanimity. This is why Stoicism is neither politically quietist — in Rome both slaves (Epictetus) and emperors (Marcus Aurelius) translated it into their own lives — nor obsolete; it is widely seen as a philosophical grandparent of modern cognitive-behavioural therapy.

Zeno's own writings are lost; his teaching reaches us through Chrysippus, Diogenes Laertius, and the later Roman Stoics. The Stoa fed indirectly into Christian ethics, into Spinoza, into Kant's idea of duty, and into today's literature on resilience and emotional self-regulation.