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.
They arrived in Thrace forty days after the revolt of Potidaea.
The Athenians also immediately received the news of the revolt of the cities. On being informed that Aristeus and his reinforcements were on their way, they sent two thousand heavy infantry of their own citizens and forty ships against the places in revolt, under the command of Callias, son of Calliades, and four colleagues.