A Dictionary of Greek and Roman biography and mythology

(Εὐρύμαχος), grandson of another Eurymachus and son of Leontiades, the Theban commander at Thermopylae, who led his men over to Xerxes. Herodotus in his account of the father's conduct relates, that the son in after time was killed by the Plataeans, when at the head of four hundred men and occupying their city. (Hdt. 7.233.) This is, no doubt, the same event which Thucydides (2.1_7) records as the first overt act of the Peloponnesian war, B. C. 431. The number of men was by his account only a little more than three hundred, nor was Eurymachus the actual commander, but the enterprise had been negotiated by parties in Plataea through him, and the conduct of it would therefore no doubt be entrusted very much to him. The family was clearly one of the great aristocratical houses. Thucydides (2.2) calls Eurymachus "a man of the greatest power in Thebes."

[A.H.C]