Summer [II 1–32]

This marks the beginning of the war between the Athenians and the Peloponnesians and the allies on each side, the point from which they only dealt with each other through heralds and were continuously at war once they had started. Events have been recorded in the order of their occurrence, by summers and winters.

The Thirty Year Treaty made after the capture of Euboea remained in force for fourteen years; but in the fifteenth year – that is, when Chrysis had been priestess at Argos for forty-eight years, when Aenesias was ephor at Sparta and Pythadorus still had two months to serve as archon at Athens, in the sixth month after the Battle of Potidaea and at the start of spring – some 300 or more Thebans led by the boetarch Pythangelus son of Phyleides and Diemporus son of Onetorides made an armed entry during the first watch of night into Plataea, a Boeotian city allied to the Athenians. A group of Plataeans invited them in and opened the gates for them – these were Naucleides and his followers, who for reasons of personal ambition wanted to do away with their political opponents and make the city over to the Thebans. They arranged this plan through Eurymachus son of Leontiades, one of the most powerful men in Thebes. The Thebans foresaw that there would be a war and wanted to take the initiative and seize Plataea – which had always been at odds with them – while the peace still held and war had not yet been openly declared. This is why they found it relatively easy to get in unobserved, because no guard had yet been established.