As early as August 430 B.C. Athens sent a peace embassy to Sparta. It was fruitless, and the war continued. In the following winter Potidaea capitulated, and next year two remarkable naval victories at Chalcis and Naupactus at the mouth of the Corinthian Gulf, won by Phormio, the Nelson of Athens, further cheered the Athenians. In September 429 B.C. Pericles died, and when in the June following, Mitylene, chief city of Lesbos, revolted, the very truth of the dead statesman's main contention, that Athens' mari time empire was unassailable, seemed questionable. It was how ever soon triumphantly vindicated. The Spartan admiral Alcidas, sent a year later to redeem a promise of help to the rebels, was a coward and fled back home of ter a hurried raid on Ionia at a mere glimpse of two Athenian warships. Mitylene surrendered at discretion in July 427 B.C. The city was cruelly punished, though more mercy was shown than pleased an Athenian poli tician then coming into prominence, Cleon "the tanner," bete noire of the playwright Aristophanes. In August 427 B.C. Plataea at last surrendered, when its tiny garrison was on the brink of perishing of hunger. At the insistence of their Theban enemies the Plataeans were slaughtered in cold blood and their city was utterly destroyed. Corcyra was finally secured for Athens by its democratic faction amid scenes of unspeakable barbarity, con summated in 426 B.C. by a ferocious massacre. But the whole war languished and drew near to stalemate.
At last, in 426 B.C., Athens bestirred herself, under direction of Cleon and of Demosthenes, the latter her best tactician in the war. The new leaders, though always hampered by the wealthy and influential Nicias, trusted chief and representative of the bourgeoisie, initiated a strategy of offence far more vigorous than the Periclean. Sicily, Boeotia, the Peloponnese itself, were all to be spheres of Athenian activity. To meet the cost, Cleon in 425 B.C. largely increased the tribute imposed on all members of the empire, in many cases up to or even beyond so%. In June 426 B.C. Demosthenes with a handful of Athenian troops proceeded to Acarnania, ostensibly to consolidate Athenian influence in the district at the expense of Ambracia, Sparta's chief ally there. His real hopes were centred upon an invasion of Boeotia by way of Phocis in co-operation with the main Athenian army which, under Nicias, was to invade by way of Tanagra on the south-east and threaten Thebes directly. The plan was a dismal failure. Demosthenes with his large army of local levies without any real stiffening by Athenian hoplites was trapped in the heart of the forests of Aetolia at Aegitium at the very outset of his enterprise, and his whole force was cut to pieces by the natives. He himself barely escaped with his life to the Athenian base at Naupactus, whence he did not dare to return to Athens to become the scape goat of the people's indignation. Nicias won an insignificant victory at Tanagra and then withdrew. Sparta entered on vigor ous reprisals. A large army under Eurylochus marched from Delphi, threatened Naupactus (which Demosthenes secured just in time), and laid siege eventually to Amphilochian Argos, Athens' ally on the Ambraciot gulf. Then Demosthenes redeemed his reputation. Two brilliant victories, those of Olpae and Idomene, won by tactical devices novel in the humdrum warfare of the time, finally destroyed all Peloponnesian and Ambraciot influence in the entire district and shattered Spartan honour. Though Acarnanians and Ambraciots henceforward observed the war from a distance, the way was henceforth clear for Athenian ships to Sicily, and Demosthenes returned in triumph to Athens.
Next year, 425 B.C., Athens, thanks to Demosthenes and Cleon, achieved the "crowning mercy" of Sphacteria. A fleet en route for Sicily put in to Navarino bay and Demosthenes built and himself garrisoned a rude fort here on Pylos promontory. The
angry Spartans came down upon him by land and sea. He beat off the assault on the fort, and the Athenian fleet returning on his summons from its slow voyage to the north penned up the Spartan navy in the bay and cut off a Spartan force landed on the island of Sphacteria from all hope of rescue. A temporary armistice secured to Athens the peaceful surrender of the hostile fleet, which she refused to return when negotiations were broken off. So Sparta for a dozen years ceased to have a fleet in being. The blockade of the island was protracted, and the approach of winter seemed likely to secure the escape of the garrison. Cleon, appointed general upon Nicias' pusillanimous, even malignant, resignation, brought Demosthenes needful reinforcements, and the latter, landing at last in overwhelming numbers on Sphacteria, overcame the Spartans' heroic resistance and brought the remnant of survivors, 292 in all, alive as prisoners to Athens. The moral effect c,f their surrender was prodigious throughout the Greek world. Not until the victory of Mantinea seven years later did Sparta wipe out the disgrace. Strategically the effect was to saf e guard Attica from all invasion, so long as Spartan prisoners were in Athens' dungeons. Sparta now in her turn sued for peace, which Cleon refused.
Then came the black year, 424 B.C. All the Athenians' main offensive schemes miscarried. In the spring a congress held at Gela, persuaded by the Syracusan statesman Hermocrates, de cided to adopt the "Monroe doctrine" of Sicily for the Sicilians, and the Athenian admirals had no choice but to return home, where they were heavily punished for a quite unavoidable failure. In the summer the renewed plan of a converging attack on Boeotia, this time from three sides, resulted in November in a crushing defeat of the main Athenian army at Delium, inflicted by the resolution and tactical ability of the Theban Pagondas. His device of a deepened wing and his skilful use of cavalry for shock tactics anticipated the coming renown of the Theban army under Epaminondas. Meanwhile an attempt to capture Megara by treachery had been frustrated when on the very point of success by the sudden dash to the city's rescue by Sparta's greatest soldier Brasidas, and only Megara's port Nisaea remained in Athenian hands. Then Brasidas completed the discomfiture of the Athenian "Second Offensive." Marching at top speed through Boeotia and Thessaly he appeared in the early winter in Chalcidice, the Achilles-heel of the Athenian empire, offering liberty and protection to cities revolting against the tyrant Athens. Am phipolis quickly surrendered herself, and the historian Thucyd ides, then in naval command in the north Aegean, arrived in hot haste from Thasos only in time to save Eion at the Strymon's mouth. Cleon's vengeance punished him unjustly with zo years' exile. Athens sought to check Brasidas' triumphant progress by concluding a truce, the "Truce of Laches," in April 423 B.C., with Sparta, whose only anxiety was to recover the prisoners of Sphacteria. Brasidas paid no heed, taking Scione and Mende defiantly. The indignant Athenians hurried reinforcements to what was now the only scene of active war. Nicias recovered Mende this year, and in 422 B.C. Cleon hoped to end the matter. To carelessness in a reconnaissance outside Amphipolis he added cowardice. Brasidas sallied from the city, routed the enemy, and Cleon himself was slain. But the Spartan, like Wolfe, fell in the moment of victory. So the two great advocates of bitter war unexpectedly perished, and Nicias was able, on April i r, 421 B.C., to conclude with Sparta that peace, called after his own name, which he hoped would end the Peloponnesian War for all time.