History of the Peloponnesian War
Thucydides
Thucydides. The history of the Peloponnesian War, Volume 1-2. Dale, Henry, translator. London: Heinemann and Henry G. Bohn, 1851-1852.
But the Chalcidians were also very anxious to have him, as a man who both appeared, while in Sparta, to be active in every thing, and after he had gone from home, proved himself most valuable to the Lacedaemonians.