During the Corcyran/Corinthian war (c. 433 B.C.), the Corinthians had captured about a thousand Corcyrans. Of these, about 800 were slaves, who the Corinthians sold. But about 250 were prominent citizens, who the Corinthians cultivated in hopes of creating a pro-Corinthian oligarchic party. In this they were successful. The prisoners returned in 427 B.C. and tried to persuade the Corcyrans to break their alliance with Athens and join forces with Corinth, but the assembly voted it down. The pro-Corinthians then charged the democratic and pro-Athenian leader with treason for seeking to "enslave" Corcyra to Athens. He was acquitted and retaliated by prosecuting them for sacrilegious trespass on the sacred grove and had an impossibly large fine assessed. Fearing an offensive and defense alliance with Athens, the oligarchs then burst in on the council (dominated by the pro-Athenian faction) and killed the pro-Athenian leader and 60 others. Only a handful escaped. The oligarchs then summoned the assembly and told them that they had only acted to save Corcyra from Athenian "tyranny." The assembly, presumably threatened and intimidated, voted to become neutral. Civil war soon broke out.
Both sides offered freedom to any slave who would join them. The great majority of slaves joined the democratic side. Thucydides reports this fact without comment, so we can only guess at the slaves' motives. Did they calculate that if freed, the would be, at best, poor citizens and as such better off in a democracy than an oligarchy? Or were they, too, moved by talk of democratic freedom and eager to share in it? Full-scale fighting ensued, with the democrats triumphant. Women joined in the fighting by climbing on roof tops and and throwing tiles; Thucydides praises their courage. The oligarchs burned their arsenal and surrounding properties to cover their retreat.
About this time, twelve Athenian ships pulled into harbor, and their commander, not wanting upheaval in an important ally, arranged a settlement between them. It proved short-lived. The democrats asked him to leave five ships and crews behind to prevent another outbreak and offered to send five ships of their own as replacements. The Athenians agreed. The Corcyrans then sought to make the oligarchs serve on the five ships as a discreet way of exiling them. The oligarchs feared they were being sent to an execution and refused to go. The democrats sought to kill them but were restrained by the Athenian commander. Over 400 oligarchs fled to sanctuary.
About this time the Corcyrans were distracted by the arrival of 53 Peloponnesian ships, to the Athenians' twelve. Although the Corcyrans had 60 ships of their own, they were not much use because two deserted and the crews of many other began fighting among themselves. The Peloponnesians prevailed in the naval battle, but the Athenians managed an orderly retreat, and the Peloponnesians failed to follow up with an attack on land. Nonetheless, the Corcyrans were in such terror that they negotiated to allow some of the oligarchs to leave sanctuary to join in the city's defenses. When 60 Athenian ships arrived, the Peloponnesians fled. The Corcyran democrats then proceeded with a general massacre of the oligarchs, including some they had persuaded to leave the sanctuary and join the defense of the island. They persuaded some of the oligarchs who had taken refuge in the temple to leave and stand trial, but the verdict was predetermined as guilty and the sentence as death. Many of the suppliants killed themselves or each other rather than submit. A general slaughter prevailed, with many private grudges being paid off, while the Athenians passively allowed it to proceed.
About 500 oligarchs escaped. They settled down on the mainland, raiding and plundering, and blockading the island and seeking support from Sparta and Corinth to restore them to power. Unable to procure such help, the oligarchs, joined by foreign mercenaries and numbering about 600, sailed back to the island and burned their boats to keep themselves from retreating. They established a fort and made sallies forth, laying waste to the countryside.
This state of affairs continued for about two years. By 425 B.C., Corcyra was suffering serious famine, and sixty Peloponnesian ships were on their way to support the oligarchs. The Athenians ordered their admirals in the course of sailing to Sicily, to stop by and see what they could do for the democrats. The Athenians marched against the oligarchs' stronghold and captured it. The oligarchs surrendered, agreeing to be sent to Athens for trial. We will never learn what the outcome would have been because the trial never took place. The Corcyrans, fearing that the Athenians would not execute the oligarchs, sent in a provocateur to convince the oligarchs to attempt to escape. This broke the terms of their surrender, so the Athenians turned them over to the tender mercies of the Corcyrans. The Corcyrans locked them in a large building and then led them out, twenty men at a time. At first the prisoners simply thought that they were being taken to another prison. When the realized that the men being removed were being killed, they barricaded the door and vowed to resist to the utmost. The Corcyrans then took the roof off and began stoning and shooting arrows at the captives inside. Many captives took their own lives. There were also women captured at the fortress; the Corcyrans sold them as slaves. Thus, says Thucydides, did the civil war end, because one side ceased to exist. Thucydides regards the Athenian commanders as much to blame. They were on their way to Sicily and made clear that they did not want anyone else to get credit for taking the captives back to Athens. As such, they rather strongly encouraged the Corcyrans to take the captives off their hands and winked at whatever they might choose to do.
Thucydides uses this ghastly civil war as the occasion for his famous comments (too long to quote in full) about how the war generally undermined basic morality:
When troubles had once begun in the cities, those who followed carried the revolutionary spirit further and further, and determined to outdo the report of all who had preceded them by the ingenuity of their enterprises and the atrocity of their revenges. The meaning of words had no longer the same relation to things, but was changed by them as they thought proper. Reckless daring was held to be loyal courage; prudent delay was the excuse of a coward; moderation was the disguise of unmanly weakness; to know everything was to do nothing. Frantic energy was the true quality of a man. A conspirator who wanted to be safe was a recreant in disguise. The lover of violence was always trusted, and his opponent suspected. He who succeeded in a plot was deemed knowing, but a still greater master in craft was he who detected one. On the other hand, he who plotted from the first to have nothing to do with plots was a breaker up of parties and a poltroon who was afraid of the enemy. In a word, he who could outstrip another in a bad action was applauded, and so was he who encouraged to evil one who had no idea of it. The tie of party was stronger than the tie of blood, because a partisan was more ready to dare without asking why.Everywhere, rival factions in cities sought foreign intervention, the democrats from Athens and the oligarchs from Sparta. All restraint was abandoned. Corcyra, Thucydides makes clear, was the first city to experience such horrors, but by no means the last. Thucydides never more clearly sets forth the ideological nature of the war, although it is possible that the ideological dimension was less strong at the beginning of the war than it later became.
A few points here are worth making. It is entirely possible that the oligarchs in Corcyra, like the Thebans in Platea, were not just being self-serving, but sincerely believed that the people would be happy to submit to an oligarchy (and a pro-Corinthian or pro-Theban one at that) if only it would free them from the horrors Athenian hegemony. If so, the oligarchs in both cases seriously miscalculated.
Thucydides makes clear that although Corcyra was the first city to experience the horrors of civil war, it was by no means the last. Yet he gives no other examples, at least as far as I have read. But he does recount at least one serious domestic atrocity by an oligarchy in shoring up its power, the previously mentioned preemptive massacre by the Spartans of some 2000 helots believed to be potential rebels. That massacre differs from the Corcyran massacres of oligarchs in that it did not take place in a civil war, and that it was undertaken out of fear rather than anger, and without provocation. But most importantly, comparing the atrocities points up a certain asymmetry between democrats and oligarchs. The oligarchs, at worst, can crush the democrats by brute force and reduce them to absolute subjugation. The democrats can exterminate the oligarchs altogether. The Spartans needed the helots because someone had to till the fields and for the oligarchy to do so would be the end of its status as an oligarchy. The Corcyran people, when the chips were down, ultimately did not need their oligarchs. Besides, the common people, being more numerous, can absorb greater losses. In the first outbreak, the Corcyrans killed 400 oligarchs who had taken refuge in the temple and an undetermined number of others, while some 500 escaped. Once these were killed, the oligarchs ceased to matter because there were none of them left. By contrast, the slaughter of 2000 helots did not even put a serious dent in their numbers. As the war grinds on, we will see Athens in adversity show a most extraordinary resilience, a resilience that has to come in large part from having a citizen body large enough to absorb major losses.
Finally, there was no happy ending here. In Corcyra, the democrats prevailed. But when democracy cannot stop a civil war from happening, then democracy has failed regardless of the outcome. The democracy that survives by the extirpation of its rivals is not worth having.