History of the Peloponnesian War (1.56.2-1.57.2)

While the Corinthians were contriving how to avenge themselves on them, the Athenians, suspecting their hostility, ordered the Potidaeans, who live on the isthmus of Pallene, being colonists of the Corinthians, but their own subjects and tributaries, to throw down the wall towards Pallene, and give hostages; and to dismiss, and not receive in future, the magistrates [*] whom the Corinthians used to send every year; being afraid that they might revolt at the instigation of Perdiccas and the Corinthians, and lead the rest of their allies Thrace-ward [*] to revolt with them.

These precautionary measures with regard to the Potidaeans the Athenians began to adopt immediately after the sea-fight at Corcyra.

For the Corinthians were now openly at variance with then; and Perdiccas the son of Alexander, king of the Macedonians, had been made their enemy, though he was before an ally and a friend.