If you had travelled through Greece in the middle of the fifth century before Christ, the two most powerful states you passed through would have struck you as barely belonging to the same civilisation.
Athens was a port. It had a fleet, an empire of tribute paying islands, a busy foreign population, an assembly that argued in public, and a habit of putting up buildings and plays that it expected the rest of the world to admire. It made its living from the sea and it was, by the standards of the time, an open place.
Sparta had no walls. It did not need them, because it had the best infantry in Greece, and because a Spartan citizen's whole life was arranged around producing that infantry. Boys were taken from their families at seven and raised in a communal system of training and deliberate hardship. Men ate in common messes into middle age. There was no coinage worth hoarding, little art, and almost no writing. Two kings ruled at once, checked by a council of elders and by five annually elected overseers who could put a king on trial.
And underneath the Spartan citizen body was the thing that explains most of Sparta's behaviour. The land was worked by helots, an enslaved population descended from the conquered inhabitants of the region next door. They outnumbered their masters by a wide and frightening margin.
Every year, the Spartan overseers formally declared war on the helots. The reason given by an ancient writer is that this let a Spartan kill one without incurring religious pollution. A state that has to renew a declaration of war on its own workforce annually is a state organised around a fear, and that fear shaped how far from home Sparta was ever willing to send its army, and for how long.
The war that began in 431 is usually called the Peloponnesian War, and our knowledge of it comes overwhelmingly from one man.
Thucydides was an Athenian, a general, and a failure at the job. He was exiled after losing a city he had been sent to protect, and he spent the next twenty years writing the history of the war he had been thrown out of. He is careful, sceptical, uninterested in oracles, and open about his method, which included admitting that he could not remember the exact words of speeches and had written what the occasion seemed to require.
His explanation for the war is famous and worth quoting closely. The immediate quarrels, he says, were disputes over a colony in the north west and a trade embargo against a small neighbour. But the truest cause, the one least talked about openly, was that Athens was becoming powerful and this frightened Sparta into fighting.
It is worth putting the immediate quarrels back in, because they show how a structural fear turns into an actual war. Corcyra, a strong naval power in the north west, fell out with its mother city Corinth and asked Athens for an alliance. Athens gave it a limited one, and Athenian ships ended up fighting Corinthian ships. Corinth was a member of the Spartan alliance and began pressing Sparta to act. Athens then barred the small city of Megara, another Spartan ally, from every harbour in its empire, which was an act of economic strangulation short of war. Sparta demanded the decree be lifted. Athens refused, on the argument that giving way to one demand invites the next. Both of those positions are recognisable, and neither is mad.
That is a claim about structure rather than blame, and it has been picked up by modern strategists as if it were a law. It is worth remembering that it is one participant's interpretation, written by a man with reasons to see the war as inevitable rather than as something Athens chose. The states involved made choices repeatedly, including several chances to stop.
Athens could not beat Sparta on land. Sparta could not beat Athens at sea. The war was therefore a problem of how to make the other side give up.
Pericles, the man who dominated Athenian politics at the outbreak, had an answer that was correct and almost unbearable. Do not fight them in the fields. Bring the rural population inside the city walls, let the Spartans burn the farms, and use the fleet to raid their coast and keep the tribute coming. Athens was joined to its port by two long walls, so as long as it held the sea it could be fed indefinitely.
So the farmers of Attica came inside and watched from the ramparts while their olive trees, which take a generation to replace, were cut down. Thucydides says they took it very badly, and it is not hard to see why.
Then in the second year the crowded city was hit by an epidemic. It killed, by Thucydides' own estimate, something like a third of the population, including Pericles himself. Thucydides caught it and survived, and left a clinical description of the symptoms so precise that doctors have been arguing about the pathogen ever since. Typhus, typhoid, smallpox, viral haemorrhagic fever and several others have all been proposed. A study of dental pulp from a mass grave pointed to typhoid, and other specialists disputed the finding. We do not know.
What the plague did to the war is easier to state. It removed the one politician with the authority to hold an unpopular strategy in place, and it left a city that had lost a third of its people and none of its ambitions.
The middle of the war produced two episodes that are still taught, because they show a democracy reasoning about power with the restraints off.
A subject city on the island of Lesbos revolted. The Athenian assembly voted to execute its entire adult male population and enslave the women and children, and sent a ship. The next day it met again, heard the argument that the punishment was both cruel and stupid, since it gave every future rebel a reason to fight to the end, and reversed itself. A second ship rowed through the night and arrived just in time. The city's ringleaders were executed instead, more than a thousand of them.
Sixteen years later a small neutral island called Melos refused to join the Athenian empire. Thucydides writes the negotiation as a dialogue, and in it the Athenian envoys drop the language of justice entirely. Justice, they say, is a question between equals in power; as things stand, the strong do what they can and the weak suffer what they must. Melos refused anyway. Athens took the island, killed the men and sold the rest.
That dialogue is the most quoted passage in ancient historical writing, and it is also the passage where a reader should be most careful. Thucydides was not present. He is reconstructing, and he has placed this exchange immediately before the disaster that follows, which is a novelist's arrangement as much as a historian's.
In 415 the Athenian assembly voted to send a fleet to Sicily, to intervene in a quarrel between cities on an island several days' sail away, at a moment when the war at home was in an uneasy truce.
It was an enormous force and it was a catastrophe. The commanders quarrelled, the most capable of them was recalled to face a religious charge and defected to Sparta instead, reinforcements were sent after the first force was already in trouble, and in the end the fleet was destroyed in the harbour of Syracuse and the army was cut to pieces retreating overland. The survivors were put to work in stone quarries until most of them died.
Thucydides gives the number of Athenian and allied dead in the tens of thousands and says that of the many who set out, few came home. Ancient casualty figures are almost never reliable, but the strategic result is not in doubt. Athens had thrown away a fleet, an army and a decade of reserves on a war of choice, and its subject cities began to calculate.
What finished Athens was money from an unexpected direction. Sparta, which had no navy worth the name, obtained Persian gold and used it to build one. It took the Spartans years to learn to use it. In 405 their fleet caught the Athenian ships beached and unprepared at Aegospotami and took almost all of them. Without a fleet, Athens could not be fed. It surrendered in 404, and the Long Walls were pulled down.
Sparta had won, and it had won by borrowing money from the Persian Empire, which the Greeks had spent the previous century congratulating themselves on defeating.
It then installed a junta in Athens, remembered as the Thirty, which killed perhaps fifteen hundred people in a matter of months before the democrats came back and threw it out. The restored Athenian democracy passed an amnesty, one of the earliest recorded, forbidding prosecution for acts committed under the junta. It kept to it, mostly. Five years later it tried and executed Socrates, which is the subject of the previous chapter, and it is fair to read that trial partly as the amnesty leaking.
Sparta's own victory lasted a little over thirty years. A state whose citizen numbers were shrinking, whose economy was worked by a hostile enslaved population, and which now had to garrison an empire it had no institutions to run, was not built for what it had won. In 371 a Theban army broke the Spartan line at Leuctra, and shortly afterwards the Thebans marched into the region Sparta had held for centuries and freed the helots. Sparta was never a great power again.
The longer result was that the Greek city states spent the fourth century exhausting one another, and that when a kingdom to the north under a competent and patient king began absorbing them one by one, they could not combine in time.
Firm: the chronology and the outcomes. We have Thucydides for the first twenty years, Xenophon for the rest, and inscriptions recording treaties, tribute assessments and casualty lists carved by the Athenians themselves. That skeleton is solid.
Soft: the speeches. Thucydides tells us he composed them, and the most quoted passages in this chapter are the ones least likely to be transcripts. They are evidence for how a thoughtful Athenian in the 390s understood power. They are not recordings.
Soft: the numbers. Plague mortality, Sicilian casualties and the size of fleets all come from a literary source with no census behind it, and ancient writers routinely inflate.
Soft: Sparta itself. Almost everything we know about the Spartan system was written by outsiders, several of whom admired it and were describing an idealised version. The word for their training system, the details of the secret police that terrorised the helots, and the famous exposure of weak infants all rest on thinner evidence than their fame suggests.
Unresolved: whether the war was avoidable. Thucydides says the growth of Athenian power made it necessary. But necessity is what people reach for after the fact, and the record shows a long series of decisions, several of them narrowly taken, any of which could have gone the other way. A reader is entitled to be less certain than the man who was there.