Zeno of Citium, after being shipwrecked near Athens and studying under the Cynic Crates and later the Megarians and philosophers of Plato's Academy, founded Stoicism around 300 BCE by teaching publicly in the Stoa Poikile in the Athenian agora. He synthesized Cynic ethics, Heraclitean physics, and Megarian logic into a unified system holding that virtue is the sole good, that living "in agreement with nature" is the goal of life, and that the cosmos is pervaded by a rational, providential principle (logos).
Intellectual setting
Zeno arrived in Athens around 312 BCE after a shipwreck, and studied successively with the Cynic Crates, the Megarian dialecticians, and philosophers of Plato's Academy before founding his own school around 300 BCE. He taught publicly in the Stoa Poikile rather than in a private garden or gymnasium, reflecting Stoicism's origins as an accessible, market-adjacent philosophy in early Hellenistic Athens.
Key ideas
Virtue as the sole good, and living in agreement with nature
Zeno held that virtue alone is genuinely good and vice alone genuinely bad, with health, wealth, and reputation merely "preferred indifferents"; the goal of life (telos) is to live in agreement with nature, meaning both one's own rational nature and the rational order of the cosmos as a whole.
A providential, rational cosmos (logos)
Drawing on Heraclitus, Zeno taught that the universe is pervaded and governed by an active, rational, fiery principle (variously called logos, pneuma, or god) that orders all things providentially, so that ethics, physics, and logic form a single coherent system rather than separate inquiries.
Legacy
Zeno's school, led after him by Cleanthes and then by Chrysippus (who systematized and greatly expanded Stoic logic and physics), grew into one of the dominant philosophical movements of the Hellenistic and Roman worlds, shaping later Roman Stoics such as Seneca, Epictetus, and Marcus Aurelius, and continuing to influence ethical thought, including modern cognitive-behavioral therapy's acknowledged debt to Stoic theories of judgment and emotion.