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.

So they set about preparing the fortifications, and in consequence of this Samos, which in any case would soon have been ready, was more quickly fortified. Not long afterward came the letter from Alcibiades, saying that the army was being betrayed by Phrynichus and that the enemy would soon attack.