In Books 6 and 7 Thucydides’ narrative is, as Plutarch puts it, ‘at its most emotional, vivid, and varied’ as he describes the Sicilian Expedition that ended so catastrophically for Athens (415-413 BCE). Book 6 features tense debates both at Athens, with cautious Nicias no match for risk-taking Alcibiades, and at Syracuse, with the statesmanlike Hermocrates confronting the populist Athenagoras. The spectacle of the armada is memorably described; so is the panic at Athens when people fear that acts of sacrilege may be alienating the gods, with Alcibiades himself so implicated that he is soon recalled. The Book ends with Athens seeming poised for victory; that will soon change, and a sister commentary on Book 7 is being published simultaneously. The Introduction discusses the narrative skill and the part these books play in the architecture of the history. Considerable help with the Greek is offered throughout the Commentary.