Xenophon, an Athenian soldier writing after Thucydides, continues his Hellenica in Book 5. These volumes follow Greek history after the Peloponnesian War into the fourth century. By Book 4, Sparta’s postwar supremacy was already cracking: Persian gold had rebuilt Athens’s walls, and light troops had cut a Spartan unit to pieces near Corinth.

In 387 BC Artaxerxes II, the Persian king, dictates the King’s Peace: every Greek city is to stand alone, which means Sparta may break any league but her own. Book 5 is how Sparta polices that peace, and how Thebes learns to hate it. Phoebidas, marching toward Olynthus in the north, seizes the Cadmea, Thebes’s citadel, in peacetime. Agesilaus, the Spartan king, will not give it back. Olynthus is squeezed until it yields. Sphodrias bungles a night raid on the Piraeus, Athens’s harbor, and is acquitted because his son is Agesilaus’s beloved. Athens founds a second confederacy. Pelopidas and the Theban exiles come home through snow and kill the polemarchs — Thebes’s collaborating magistrates — at a drinking party. The great battle at Leuctra is still ahead, but the road to it is already open.