History of the Peloponnesian War
Thucydides
Thucydides, Vol. 1-4. Smith, Charles Foster, translator. London and Cambridge, MA: Heinemann and Harvard University Press, 1919-1923.
He had namely first laid up for himself with the King a store of gratitude in the following circumstances, and thus had begun the whole affair.
When he was in that quarter before, after the return of the Hellenic fleet from Cyprus,[*](cf. Thuc. 1.94.2.) he had taken Byzantium, then in the possession of the Persians, and certain connections and kinsmen of the King were captured in the place when the city fell. These prisoners he sent back to the King without the knowledge of the allies in general, whom he gave to understand that they had escaped from him.
And he was carrying on this intrigue in concert with Gongylus the Eretrian, the very man whom he had placed in charge of Byzantium and the captives. And he also sent a letter by Gongylus to the King, in which the following was written, as was afterwards discovered: