In 399 BC two men stood uneasily at the edge of Sparta’s marketplace. One was a revolutionary, the other an informer. The market was crammed with slaves and wares, the result of Sparta’s hegemony following its victory in the Peloponnesian War five years before. They may have seen Agesilaus, a new Spartan king, glad-handing his way through the market, accompanied by the ephors, the five magistrates who oversaw the state. So confident was he in Sparta’s supremacy that he was preparing for an expedition against the Persians. No Greek state had ever achieved the hegemony Sparta was enjoying, but, just 28 years later, Sparta would be defeated entirely and relegated to permanent irrelevance. These two men, looking out on the marketplace that day, were not responsible for Sparta’s dramatic decline: they were its symptoms.

Only the name of the revolutionary is known: Kinadon. He was a trusted soldier in the Spartan army who had performed many tasks for the ephors. He was not, despite all this, a Spartan citizen or homoios (literally, equal). He was a hypomeion, a lesser, a Spartan who was unable to pay the dues for the communal messes where the homoioi dined together. He could not vote in Sparta’s assembly or participate fully in the state’s social life. In status-obsessed Greece he was atimos: dishonoured and disenfranchised.

Kinadon asked his friend how many people he could see in the market. “Four thousand” his friend replied. Kinadon asked how many of those 4,000 were homoioi? His friend frowned, and counted for a long time. Including the king and the ephors, he could count, in the commercial hub of Greece’s most powerful state, 40 citizens.

“Believe” said Kinadon, “that those 40 men are your enemies, and those 4,000 your allies.” He told him that so many others: the helots, the slave peoples kept on Spartan estates, the perioikoi, from nearby cities, and other hypomeiones like himself could not keep themselves from eating the Spartans raw. He took his friend on a tour through the metal market of the city, pointing out the weapons for their uprising: sickles, hatchets, knives. In the fields and the forests, chisels and saws would do.

The reason that Kinadon and his friend only saw 40 citizens is because Sparta was suffering from what Aristotle termed oliganthropia, a shortage of manpower. This was partly caused by their losses in the Peloponnesian war, plague and a particularly powerful earthquake. But, as the 4,000 in the agora attest, it was not that Sparta lacked men, it was that they lacked homoioi.

Sparta once had, by Greek standards, a large citizen body. In 496 BC Herodotus claims it had 8,000 homoioi. That this had been reduced to around 1,000 by 371 BC was not so much about deaths, but about many Spartans, like Kinadon, no longer being able to afford the communal mess fees. This was not because Sparta had grown poorer, quite the opposite, but because wealth and land had become concentrated among Sparta’s elite.

Sparta’s origins were so egalitarian, they would have made the Soviets blush and the Nazis despair, a particular irony given that Sparta was held up by Hitler as a model for National Socialism.  The founding legend went that Lycurgus, Sparta’s great, semi-mythical lawmaker, had split the land entirely equally among its citizens. This may have been an anachronistic exaggeration, but it is certainly true that Spartan wealth was far more equally distributed at the start of the fifth century BC: in 404 BC restrictions of the private use of foreign gold and silver currency were relaxed and laws against the gift of land were lifted. The removal of these measures, which had restrained inequality, at a time when victorious Sparta was flush with newly-acquired wealth, allowed capital-rich and well-connected Spartans to buy up land, further concentrating the wealth among fewer and fewer, richer and richer homoioi. Those, like Kinadon, who could not afford the annual dues, became hypomeiones. And so it was, as Aristotle records, that a territory that could have supported 15,000 cavalry and 30,000 infantry, could not even furnish 1,000 homoioi.

Because of the shortage of homoioi, It was the perioikoi and helots that composed much of Sparta’s armies. The homoioi were acutely aware of their precarious position, vastly outnumbered by their disenfranchised subject peoples, and ruled through terror. The Krypteia, a proto-secret-police, roamed the lands of the helots, killing those out after curfew. The Spartans were terrified of a helot uprising and obsessed with keeping them weak: in 425 BC 2,000 helots were offered the chance to volunteer to serve in the Spartan army, taken a few miles away and slaughtered. Dissenters and fomenters were ruthlessly snuffed out, and this is what happened to Kinadon.

Kinadon misjudged his confidence in his friend that day, who soon informed King Agesilaus and the ephors. Kinadon was captured and the conspiracy’s leaders rounded up and killed and the episode is recorded by Xenophon, a great friend of Agesilaus. But, although Kinadon’s revolt failed, Sparta would not last much longer.

Despite, or perhaps because of, the homoioi’s precarity, Sparta pursued an aggressive foreign policy, alienating almost all the key states of the region: Agesilaus’ expedition the year after Kinadon’s revolt, turned Persia from an ally into an enemy that bankrolled Sparta’s rivals. Sparta failed to reward Corinth for its support in the Peloponnesian War and botched coups in Thebes and Athens, uniting most of the Greek powers against them.

The result of Sparta’s hyper-aggressive policy was a grand coalition, led by a Theban confederation,which defeated the Spartans at Leuctra in 371 BC. The Spartans were actually able to field a larger army of ten thousand, but in this existential battle for Sparta’s future, only seven hundred were homoioi, four hundred of whom died in battle. In the following days and years, the Theban coalition swept through the Peloponnese. The Spartans were just able to keep the invading army from sacking Sparta itself, but the army ravaged Laconia and freed much of the helots and Sparta’s subject cities. Sparta limped on into the age of Alexander, but was never strong enough or populous enough to return to its previous prominence and never fully reintegrated the territories it had lost.

Sparta’s rapid decline was made inevitable by the restriction of its citizenship to a very narrow few. The stubborn exclusivity of its citizenship excluded and disenfranchised tens of thousands and stands in marked contrast to the Mediterranean’s first hegemon, Rome, whose tolerant approach to citizenship allowed rapid expansion. It is not surprising that Sparta fell: all empires do. What is striking is how a narrow group of citizens, no larger than many English villages, resisted reform, even when the consequences were obvious. The conspiracy of Kinadon showed the fragility of Sparta’s position, yet the homoioi chose to stay on a path that could only lead to decline. Sparta stands as a cautionary tale: that when a state becomes ossified, it will soon be fossilised.