History of the Peloponnesian War
Thucydides
Thucydides. History of the Peloponnesian War. Crawley, Richard, translator. London and Toronto: J. M. Dent and Sons Ltd.; New York: E. P. Dutton and Co., 1914.
In the meantime the Isthmian games took place, and the Athenians, who had been also invited, went to attend them, and now seeing more clearly into the designs of the Chians, as soon as they returned to Athens took measures to prevent the fleet putting out from Cenchreae without their knowledge.
After the festival the Peloponnesians set sail with twenty-one ships for Chios, under the command of Alcamenes. The Athenians first sailed against them with an equal number, drawing off towards the open sea. The enemy, however, turning back before he had followed them far, the Athenians returned also, not trusting the seven Chian ships which formed part of their number,