History of the Peloponnesian War

The Potidaeans and the Peloponnesians under Aristeus, in expectation of the coming of the Athenians, lay now encamped in the isthmus near unto Olynthus and had the market kept for them without the city.

And the leading of the foot the confederates had assigned to Aristeus, and of the horse to Perdiccas; for he fell off again presently from the Athenians and, having left Iolaus governor in his place, took part with the Potidaeans.

The purpose of Aristeus was to have the body of the army with himself within the isthmus and therewith to attend the coming on of the Athenians, and to have the Chalcideans and their confederates without the isthmus, and also the two hundred horse under Perdiccas, to stay in Olynthus, and when the Athenians were passed by, to come on their backs and to inclose the enemy betwixt them.