Such reasoning, hollow and false as it was, turned the scale in favour of Corcyra, and a defensive alliance was concluded, pledging the Athenians and Corcyraeans to aid each other against any attack on the territory or allies of either state. For the Athenians wished to avoid breaking the Thirty Years' Truce, and therefore refrained from entering into any agreement which might oblige them to acts of open aggression against Corinth.
There can be little doubt that Pericles, who was mainly responsible for this decision, committed a fatal error in advising the Athenians to take up the cause of Corcyra. By this act Athens incurred the implacable hostility of Corinth, and revived the old grudge which that city had conceived against her when Megara joined the Athenian alliance. In the constantly shifting currents of Greek politics, Athens might well, under wise guidance, have steered her way safely through the perils which surrounded her. The Corinthians had half forgotten their grievance, as is proved by their conduct at the revolt of Samos; and the tone of their representative at the Corcyraean debate is decidedly friendly. The Spartans were sluggish and procrastinating by nature, and required some powerful impulse to induce them to act with vigour; and this impulse was now supplied by Corinth. By accepting, therefore, the alliance of Corcyra, Athens barred the way to all compromise, and gathered into one head all the scattered causes of jealousy and hatred which had been accumulating against her in the last fifty years.
Early in the following year the Corinthian fleet, numbering a hundred and fifty sail, put to sea from Corinth, to renew the war with Corcyra, and a battle was fought off the coast of Epirus. The engagement was long and fierce, and the event was finally decided by a small squadron of Athenian ships, which had been sent with instructions to hinder any attempt of the enemy to land on the island Seeing that the Corcyraeans were being forced back upon their own coast, the Athenian captains, who had hitherto looked on, and taken no part in the battle, now assumed the offensive, and lent such effectual aid that the Corinthians were held in check until the sudden appearance of twenty additional ships from Athens, which had been sent off immediately after the others, put an end to the action. This timely interference saved Corcyra from ruin; for next day the Corinthians, after a formal remonstrance, set sail for home, taking with them two hundred and fifty prisoners, belonging to the noblest families in Corcyra, whom they kept in safe custody, but treated with great consideration, hoping by means of them at some future time to recover their influence in the island.
II
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?
"Men of Sparta, I speak as a friend, and you will not take my candour amiss. New times require new manners, and if you would maintain your great position you must move with the march of events, and abandon your old-fashioned ways. Do not mistake stagnation for stability, but learn a lesson even from these hated Athenians, who have risen to their present pitch of greatness by adapting themselves to every new need as it arose.
"You know what you have to do, if you would wipe out the reproach which rests upon you, and keep the respect of your faithful allies. Send an army into Attica, and compel the Athenians to withdraw their forces from Potidaea. And let it be done speedily, for while we are talking our kinsmen are perishing."
It happened that an Athenian embassy was present in Sparta, having been sent there on some other business, and not for the purpose of representing Athens at the debate. But when they heard of the outcry which had been raised against their city, the envoys asked permission for one of their number to address the Spartan assembly, wishing to explain the true character and origin of the Athenian Empire, and to warn the Spartans against plunging the whole country into the horrors of civil war. Leave being granted, the Athenian orator entered on his subject by sketching the course of events for the last sixty years. Athens, he said, had twice saved Greece, first at Marathon, and afterwards at Salamis. On the first of these occasions she had stood almost alone against an overwhelming force of Persians; and ten years later, though betrayed by her allies, she had borne the brunt against the navy of Xerxes. Who, then, was worthier than she to hold empire over Greeks? That empire had been forced upon her by the inertness of Sparta, and by the cowardice and sloth of her own allies in the Delian league. The power thus gained had been used with moderation, in marked contrast to the previous tyranny of Persia exercised over the same cities, and the arrogance of Spartan officers when engaged on foreign service. But a light yoke, it would seem, was harder to bear than a heavy one; if Athens had openly oppressed her subjects, she would never have heard a murmur.
Having thus tried to combat the prejudice against Athens, the orator addressed himself directly to the Spartans, and said: "Consider the awful responsibility which you will incur, if you suffer yourselves to be carried away by the invectives of your allies, and drive us against our will to tempt with you the dark uncertainties and perilous issues of war. There is still time for an amicable settlement of our differences: Athens is prepared to make all reasonable concessions, and to submit to arbitration, as the terms of the treaty direct. And if you decline to accept this offer, the guilt of the aggressor will lie with you."