History of the Peloponnesian War

In Plataea, a faction anxious to leave its alliance with Athens helps Thebes attack the city, but a counterattack by Athenian loyalists routs the Theban forces. Reinforcements arrive too late to help, after being delayed by rain that has swelled a local river, making it impassable. The victorious Plataeans kill their Theban prisoners. Athens offers refuge to Plataea’s women and children and leaves a garrison to defend the city. Sparta and Athens both believe these events represent the breaking of their treaty and prepare for war. Among the Hellenes, sentiment leans towards Sparta, whether because states want to be independent from the Athenian empire or because they fear being absorbed by it.

Thucydides lists the two sides’ allies. On the Spartan side are Megara, Boeotia, Locris, Phocis, Ambracia, Leucas, Anactorium, Corinth, Sicyon, Pellene, Elis, and all Peloponnesian states inside the isthmus, with the exception of Argos and Achaea. On the Athenian side are Chios, Lesbos, Plataea, the Messenians of Naupactus, most of Acarnania, Corcyra, Zacynthus, Ionia, the Hellespont, Thrace, the Carian coast, and all the Cyclades, except Melos and Thera.

As the Peloponnesians prepare to invade Attica, Spartan King Archidamus offers to make peace with Athens, but they refuse.