At this point Sparta decided to destroy Plataea, the Athenian outpost in Boeotia. A very brilliant description of the siege and counter-operations reveals very clearly the Spartan inability to attack walled towns and explains their objection to fortified friends. Leaving the town guarded they retired for a time, to complete the work later. The war began to spread beyond the Peloponnese to the north of the Corinthian gulf, the control of which was important to both sides. The Acarnanians were attacked by Sparta and appealed to the Athenian admiral Phormio. Two naval actions in the gulf revealed the astonishing superiority of the Athenian navy on the high seas. Threatened in her corn supply in the west, Sparta began to intrigue with the outlying kingdoms on the north-east, the "Thraceward parts" on the trade-route being the objective.
A spirit of revolt against Athenian rule appeared in Lesbos, which seceded in 428. The chief town in this non-Ionic island was Mytilene, which sent ambassadors to Sparta. Their speech clearly explains how the Athenians were able to keep their hold on their policy; her policy (like that of Rome) was to divide the allies by carefully grading their privileges, playing off the weak against the stronger. The Spartans proved unable to help and the Athenians easily blockaded the city, capturing it early in 427. In their anger they at first decided to slay all the inhabitants, but a better feeling led to a reconsideration next day. In the Assembly two great speeches were delivered. Pericles had been succeeded by Cleon, to whom Thucydides seems to have been a little unjust. He opened his speech with the famous remark that a democracy cannot govern an Empire; it is liable to sudden fits of passion which make a consistent policy impossible. He himself never changed his plans, but his audience were different.
"You are all eyes for speeches, all ears for deeds; you judge of
the possibility of a project from good speeches; accomplished facts
you believe not because you see them but because you hear them from
smart critics. You are easily duped by some novel plan, but you
refuse to adhere to what has been proved sound. You are slaves to
every new oddity and have nothing but contempt for what is familiar.
Every one of you would like to be a good speaker, failing that, to
rival your orators in cleverness. You are as quick to guess what is
coming in a speech as you are slow at foreseeing its consequences.
In a word, you live in some non-real world."
He pleaded for the rigorous application of the extreme penalty already voted.
He was opposed by Diodotus, who appealed to the same principle as Cleon did expediency.
"No penalty will deter men, not even the death penalty. Men have
run through the whole catalogue of deterrents in the hope of
securing themselves against outrage, yet offences still are common.
Human nature is driven by some uncontrollable master passion which
tempts it to danger. Hope and Desire are everywhere and are most
mischievous, for they are invisible. Fortune too is as powerful a
means of exciting men. At tunes she stands unexpectedly at their
side and leads them to take risks with too slender resources. Most
of all she tempts cities, for they are contending for the greatest
prizes, liberty or domination. It is absolutely childish then to
imagine that when human nature is bent on performing a thing it will
be deterred by law or any other force. If revolting cities are quite
sure that no mercy will be shown, they will fight to the last,
bequeathing the victors only smoking ruins. It would be more expedient
to be merciful and thus save the expenses of a long siege."
This saner view prevailed. The doctrine of a "ruling passion" is a remarkable contribution to Greek political thought, the abstract personifications reading like the work of a poet or philosopher. An exciting race against time is most graphically described. After great exertions the ship bearing the reprieve arrived just in time to save Mytilene. This act of mercy stands in sinister contrast with the treatment the unhappy Plataeans received from the liberators of Greece. The citizens were captured, Athens having strangely abandoned them in spite of her promise to help. They were allowed to commemorate their services to Greece, appealing in a most moving speech to the sacred ground of their city, the scene of the immortal battle. All was in vain. The Thebans accused them of flat treachery to Boeotia, securing their condemnation. Corcyra similarly proved unprofitable; it was afflicted by fratricidal dissensions which coloured one of Thucydides' darkest pictures. As the war went on it became clearer that it was a struggle between two rival political creeds, democracy and oligarchy. To the partisans all other ties were of little value, whether of blood or race or religion; only frenzied boldness and unquestioning obedience to a party organisation were of any consequence. This wretched spirit of feud was destined in the long run to spell the doom of the Greek cities. In 427 the first mention was made of the will-of-the-wisp which in time led Athens to her ruin. In her anxiety to intercept the Peloponnesian corn she supported Leontini against Syracuse, the leading Sicilian state. In Acarnania the capable general Demosthenes after a series of movements not quite fruitless succeeded in bringing peace to the jarring mountain tribes.
In 425 a most important event took place. As an Athenian squadron was proceeding to Sicily it was forced to put in at Pylos, where many centuries later Greece won a famous victory over the Turks. Demosthenes, though he had no official command, persuaded his comrades to fortify the place as a base from which to harry Spartan territory. It was situated in the country which had once belonged to the Messenians who for generations had been held down by the Spartan oligarchs. Deserters soon began to stream in; the gravity of the situation was recognised by the Spartan government who landed more than four hundred of their best troops on the island of Sphacteria at the entrance to the bay. These were speedily isolated by the Athenian navy; and news of the event filled all Greece with excitement. A heated discussion took place at Athens, where Cleon accused Nicias, the commander-in-chief, of slackness in not capturing the blockaded force. Spartan overtures for a peace on condition of the return of the isolated men proved vain; after a lively altercation with Nicias Cleon made a promise to capture the Spartans within thirty days, a feat which he accomplished with the aid of Demosthenes. Nearly three hundred were found to prefer surrender to death; these were conveyed to Athens and were an invaluable asset for bargaining a future peace.
A further success was the capture of Nisaea, the port of Megara, in 424, but an attempt to propagate democracy in Boeotia ended in a severe defeat at Delium; the fate of Plataea was a bad advertisement in an oligarchically governed district. Worse was to follow. Brasidas, a Spartan who had greatly distinguished himself at Pylos, passed through Thessaly with a volunteer force, reaching Thrace and capturing some important towns; the loss of one of these, Eion, caused the exile of the historian, who was too late to save it. In 423 a truce for one year was arranged between the combatants, but Brasidas ignored it, sowing disaffection among the Athenian allies. His personal charm gave them a good impression of the Spartan character and his offer of liberty was too attractive to be resisted. His success was partly due to a deliberate misrepresentation of the Athenian power which proved greater than it seemed to be. The two real obstacles to peace were Brasidas and Cleon; at Amphipolis they met in battle; a rash movement gave the Spartan an opportunity for an attack. He fell in action, but the town was saved. Cleon was killed in the same battle and the path to peace was clear. The truce for one year developed into a regular settlement in 421, Nicias being responsible for its negotiation in Athens. The chief clause provided that Athens should recover Amphipolis in exchange for the Spartan captives.
The members of the Peloponnesian league considered themselves betrayed by this treaty, for their hated rival Athens had not been humbled. Corinth was the ringleader in raising disaffection. She determined to create a new league, including Argos, the inveterate foe of Sparta. This state had stood aloof from the war, nursing her strength and biding her time for revenge. When Sparta failed to restore Amphipolis, the war party at Athens, led by Alcibiades, formed an alliance with Argos to reduce Sparta; but this policy alienated Corinth, who refused to act with her trade rival. An Argive attack on Arcadia ended in the fierce battle of Mantinea in 418, in which Sparta won a complete victory. Argos was forced to come to terms, the new league was dissolved and Athens was once more confronted by her combined enemies, her diplomacy a failure and her trump-card, the Sphacterian prisoners, lost.