History of the Peloponnesian War

The plan of Aristeus was as follows: he was to hold his own army on the isthmus and watch for the approach of the Athenians, while the Chalcidians and the other allies from outside of the isthmus[*](i.e. the Bottiaeans, who, like the Chalcidians, lived outside the isthmus.) and the two hundred horse furnished by Perdiccas were to remain at Olynthus; then when the Athenians should move against the forces of Aristeus, the others were to come up and attack them in the rear, and thus place the enemy between their two divisions.

But Callias, the commander of the Athenians, and his colleagues sent the Macedonian cavalry and a few of the allies toward Olynthus, to shut off aid from that quarter, while they themselves broke camp and advanced against Potidaea.