Xenophon, an Athenian soldier who later lived among Spartans, wrote the Hellenica, a history of Greece after Thucydides, from the last years of the Peloponnesian War into the fourth century BC. This is Book 6. Book 5 left Greece under the King's Peace of 387 BC, with Sparta garrisoning cities and Thebes throwing off that occupation; the clash had not yet been fought.

In 371, at a peace conference, Epaminondas, the Theban leader, will not sign Thebes out of Boeotia, the league of cities around Thebes that Sparta wants broken. King Cleombrotus of Sparta marches. At Leuctra, in Boeotia, the Sacred Band — three hundred Theban pairs pledged to stand together — and a left wing stacked fifty shields deep crush the Spartan right. The king dies on the field. Four hundred Spartiates, full citizens, lie there. Jason of Pherae, a Thessalian warlord, rides in as if Greece were already his, then is murdered. Thebans winter in Laconia, Sparta's own valley. Messene, homeland of the helots, the serfs Sparta had held for centuries, is refounded. Xenophon, who loved the Spartan king Agesilaus, writes the disaster without consolation.