History of the Peloponnesian War

Remaining among the Chalcidians, he continued to carry on the war; in particular he laid an ambuscade near the city of the Sermylians, and cut off many of them; he also communicated with Peloponnese, and tried to contrive some method by which help might be brought.

Meanwhile, after the completion of the investment of Potidaea, Phormio next employed his sixteen hundred men in ravaging Chalcidice and Bottica: some of the towns also were taken by him.

The Athenians and Peloponnesians had these antecedent grounds of complaint against each other: the complaint of Corinth was that her colony of Potidaea, and Corinthian and Peloponnesian citizens within it, were being besieged; that of Athens against the Peloponnesians that they had incited a town of hers, a member of her alliance and a contributor to her revenue, to revolt, and had come and were openly fighting against her on the side of the Potidaeans. For all this, war had not yet broken out: there was still truce for a while; for this was a private enterprise on the part of Corinth.

But the siege of Potidaea put an end to her inaction; she had men inside it: besides, she feared for the place. Immediately summoning the allies to Lacedaemon, she came and loudly accused Athens of breach of the treaty and aggression on the rights of Peloponnese.