Book VI begins with the Athenians voting to attack Sicily, despite their ignorance of the size of the island and despite Nicias pleas to the Athenians not to invade. Thucydides gives an intriguing overview of the history of the peoples of Sicily, including a settlement of escaped Trojans after the sack of Ilium. He goes on to discuss the founding of other minor Greek cities in Hellas.
Nicias asks for a second vote on the ill-fated Sicilian expedition. Alcibiades, however, would lead the Athenians to ruin in Sicily. Alcibiades persuades the multitude by claiming their choice is between one of conquer or be conquered. He is the voice of the Athenian empire, while Nicias is the voice of reason.
Curiously, the stone Hermae throughout the city of Athens are found all mutilated, the Mysteries profaned, and all are encouraged to come forward about any other blasphemy. Alcibiades is implicated, but the expedition is all ready to route to Sicily. He denies the charges strongly. He leaves for Sicily at once but is called back to answer the charges of blasphemy. A wild mood overtakes Athens, and Thucydides spends considerable time correcting the popular opinion of the Athenians regarding paranoia of previous tyrannies, like Pisistratus, nearly one hundred years prior. A witch hunt ensued with many implicated people being executed. In this climate, Alcibiades flees Sicily, not to return to Athens. He went as far as Thurri and then disappeared.
He flees to Sparta where he laments the absurdity of democracy, but that it has found some success in Athens. He betrays Athens and offers his knowledge as an advantage for Sparta. He takes the opposite approach of Socrates in the city of Athens. Recall Alcibiades in simpler times during Plato’s Symposium.
The book concludes as Athens and Sparta resume open conflict with one another in both Argos, as well as the Peloponnesus.