Thucydides, an Athenian who fought in this war and then wrote it, tells how Athens and Sparta tore Greece apart from 431 to 404 BCE. This is Book 6 of his History of the Peloponnesian War. The peace after Book 5 was already a cheat; Melos, a small island that stayed out, was destroyed, and Sicily was already being talked of in Athens’s port.

Book 6 is the Sicilian expedition, the gamble that broke Athens. Segesta, a Sicilian town, dangles silver that is mostly a trick and asks Athens to fight Syracuse, a Greek city as large as Athens, with cavalry Athens does not have. Nicias, cautious and rich, tries to talk the voyage down and only makes it larger. Stone roadside gods called herms are smashed in the night. Alcibiades, the spark of the plan, sails under a charge, is recalled, then jumps ship to Sparta. At Syracuse the walls race. Lamachus dies in a ditch. Gylippus, a Spartan, slips in from the Peloponnese — southern Greece — and stiffens the defense. The Athenian camp on the Great Harbor starts to look like a city under siege. Nicias writes home for another army rather than admit the thing is lost.