In the early third century BCE, on a dusty Athenian afternoon, a tall, thin man with a dark Cypriot complexion stood under the painted colonnades of the Stoa Poikile, listening. Around him, the everyday noise of the city swelled and receded: sellers shouting prices in the Agora, boys chasing one another between stalls, the distant clang of a blacksmith’s hammer. But under the shade of the stoa, the air shifted. A philosopher was speaking, and the small crowd tightened around him. The man listening—forty years old, reserved, with the stoop of someone long accustomed to reading—had come to Athens after losing almost everything in a shipwreck. His name was Zeno, from the city of Citium on the island of Cyprus, and in the years to come the philosophy he would build in this very colonnade would reshape the moral imagination of the Mediterranean world. ...