During a lull in the war between Athens and Sparta, the Athenians decided to invade and occupy Sicily. Thucydides tells us in "The Peloponnesian War" that "they were, for the most part, ignorant of the size of the island and the numbers of its inhabitants ... and they did not realize that they were taking on a war of almost the same magnitude as their war against the Peloponnesians."
According to Thucydides, the digression into Sicily in 416 BC -- a sideshow that involved lying exiles, hopeful contractors, politicized intelligence, a doctrine of preemption -- ultimately cost Athens everything, including its democracy.
Nicias, the most experienced Athenian general, had not wanted to be chosen for the command. "His view was that the city was making a mistake and, on a slight pretext which looked reasonable, was in fact aiming at conquering the whole of Sicily -- a considerable undertaking indeed," wrote Thucydides.
Nicias warned that it was the wrong war against the wrong enemy and that the Athenians were ignoring their real enemies -- the Spartans -- while creating new enemies elsewhere. "It is senseless to go against people who, even if conquered, could not be controlled," he argued.
Occupying Sicily would require many soldiers, Nicias insisted, because it meant establishing a new government among enemies. "Those who do this [must] either become masters of the country on the very first day they land in it, or be prepared to recognize that, if they fail to do so, they will find hostility on every side."
The case for war, meanwhile, was made by the young general Alcibiades, who was hoping for a quick victory in Sicily so he could move on to conquer Carthage. Alcibiades, who'd led a dissolute youth (and who happened to own a horse ranch, raising Olympic racers) was a battle-tested soldier, a brilliant diplomat and a good speaker. (So much for superficial similarities.)
Alcibiades intended to rely on dazzling technology -- the Athenian armada -- instead of traditional foot soldiers. He told the Assembly he wasn't worried about Sicilian resistance because the island's cities were filled with people of so many different groups. "Such a crowd as this is scarcely likely either to pay attention to one consistent policy or to join together in concerted action.... The chances are that they will make separate agreements with us as soon as we come forward with attractive suggestions."
Another argument for the war was that it would pay for itself. A committee of Sicilian exiles and Athenian experts told the Assembly that there was enough wealth in Sicily to pay the costs of the war and occupation. "The report was encouraging but untrue," wrote Thucydides.
Though war was constant in ancient Greece, it was still usually justified by a threat, an insult or an incident. But the excursion against Sicily was different, and Alcibiades announced a new, or at least normally unstated, doctrine.
"One does not only defend oneself against a superior power when one is attacked: One takes measures in advance to prevent the attack materializing," he said.
When and where should this preemption doctrine be applied? Alcibiades gave an answer of a sort. "It is not possible for us to calculate, like housekeepers [perhaps a better translation would be "girlie men"], exactly how much empire we want to have. The fact is that we have reached a state where we are forced to plan new conquests and forced to hold on to what we have got because there is danger that we ourselves may fall under the power of others unless others are in our power."
Alcibiades' argument carried the day, but before the invasion, the Athenian fleet sailed around seeking allies among the Hellenic colonies near Sicily. Despite the expedition's "great preponderance of strength over those against whom it set out," only a couple of cities joined the coalition.
At home, few spoke out against the Sicilian operation. "There was a passion for the enterprise which affected everyone alike," Thucydides reports. "The result of this excessive enthusiasm of the majority was that the few who actually were opposed to the expedition were afraid of being thought unpatriotic if they voted against it, and therefore kept quiet."
In the face of aggressive posturing, Nicias appealed to the Assembly members to show true courage.
"If any of you is sitting next to one of [Alcibiades'] supporters," Nicias said, "do not allow yourself to be browbeaten or to be frightened of being called a coward if you do not vote for war.... Our country is on the verge of the greatest danger she has ever known. Think of her, hold up your hands against this proposal and vote in favor of leaving the Sicilians alone."
We don't know how many Athenians had secret reservations, but few hands went up against the war.
In the end, the Athenians lost everything in Sicily. Their army was defeated and their navy destroyed. Alcibiades was recalled early on; Nicias was formally executed while thousands of Athenian prisoners were left in an open pit, where most died.
The Sicilians didn't follow up by invading Attica; they just wanted Athens out. But with the leader of the democracies crippled, allies left the Athenian League. Then the real enemy, Sparta, ever patient and cautious, closed in over the next few years. But not before Athens descended, on its own, into a morass of oligarchic coups and self- imposed tyranny.