It was not long before the effects of this impolitic breach with Corinth were sensibly felt by Athens. In the course of the following summer, Potidaea, a Corinthian colony, situated on the borders of Macedon, and included in the Athenian alliance, openly raised the standard of revolt, encouraged by promises from Sparta, and by the presence of a strong body of hoplites, sent for its support from Corinth. Potidaea was presently closely invested by an Athenian army and fleet, and the Corinthians pretended to make this a fresh ground of complaint, though they had themselves incited the city to throw off its allegiance to Athens.
Feeling that matters were now approaching a crisis, the Spartans summoned a congress of their allies, and invited all who had any grievance against Athens to state their case. Then some spoke of the wrongs of Aegina, formerly not the least among Greek cities, but now so crushed under the yoke of Athens that she had not dared to raise her voice openly against the tyrant-city. The Megarians complained of the restrictions on their commerce, which threatened them with an empty exchequer and a starving population; and others followed in the same strain. When all the rest had spoken, the Corinthian orator, who had reserved his eloquence till the end, came forward and delivered a vehement harangue, containing hardly any specific charge against Athens, but well calculated to inflame the passions and provoke the pride of the Spartans. Though the acknowledged leader of Greece, and champion of her liberties, Sparta, he said, had always been the last to see the dangers which menaced the common country, and the last to take measures for her defence. Spartan apathy and indolence had brought the Greeks to the brink of ruin in the Persian War; and when that danger was passed, the same fatal indifference had enabled Athens to advance step by step on the path of aggrandisement; until now she had grown so strong that the united force of the whole Peloponnesian league would be required to put her down. Why had not the Spartans listened to the warnings which they had heard, when the Athenians were rebuilding their walls? Then they might have stopped the evil at its source, and saved a multitude of cities from slavery and oppression. "Consider," cried the orator, warming to his subject, "what manner of men these Athenians are, and how vast is the difference between them and you. While you are shut up in this inland valley, treading the dull round of mechanical routine, they are continually pushing forward the boundaries of their empire, toiling night and day to make their city great, never satisfied with what they have, always thirsting for more. Cautious, timid, and conservative as you are, hardly to be roused from your sloth by the most imminent perils, how can you hope to curb the flight of Athenian ambition, which knows no limit, and is checked by no reverse?
