After bivouacking with the army in the precinct of Nemean Zeus, in which the poet Hesiod is said to have been killed by the people of the country, according to an oracle which had foretold that he should die in Nemea, Demosthenes set out at daybreak to invade Aetolia. The first day he took Potidania, the next Krokyle, and the third Tichium, where he halted and sent back the booty to Eupalium in Locris, having determined to pursue his conquests as far as the Ophionians, and, in the event of their refusing to submit, to return to Naupactus and make them the objects of a second expedition. Meanwhile the Aetolians had been aware of his design from the moment of its formation, and as soon as the army invaded their country came up in great force with all their tribes; even the most remote Ophionians, the Bomiensians, and Calliensians, who extend towards the Malian Gulf, being among the number.

The Messenians, however, adhered to their original advice. Assuring Demosthenes that the Aetolians were an easy conquest, they urged him to push on as rapidly as possible, and to try to take the villages as fast as he came up to them, without waiting until the whole nation should be in arms against him. Led on by his advisers and trusting in his fortune, as he had met with no opposition, without waiting for his Locrian reinforcements, who were to have supplied him with the light-armed darters in which he was most deficient, he advanced and stormed Aegitium, the inhabitants flying before him and posting themselves upon the hills above the town, which stood on high ground about nine miles from the sea. Meanwhile the Aetolians had gathered to the rescue, and now attacked the Athenians and their allies, running down from the hills on every side and darting their javelins, falling back when the Athenian army advanced, and coming on as it retired; and for a long while the battle was of this character, alternate advance and retreat, in both which operations the Athenians had the worst.

Still as long as their archers had arrows left and were able to use them, they held out, the light-armed Aetolians retiring before the arrows; but after the captain of the archers had been killed and his men scattered, the soldiers, wearied out with the constant repetition of the same exertions and hard pressed by the Aetolians with their javelins, at last turned and fled, and falling into pathless gullies and places that they were unacquainted with, thus perished, the Messenian Chromon, their guide, having also unfortunately been killed. A great many were overtaken in the pursuit by the swift-footed and light-armed Aetolians, and fell beneath their javelins; the greater number however missed their road and rushed into the wood, which had no ways out, and which was soon fired and burnt round them by the enemy. Indeed the Athenian army fell victims to death in every form, and suffered all the vicissitudes of flight; the survivors escaped with difficulty to the sea and Oeneon in Locris, whence they had set out. Many of the allies were killed, and about one hundred and twenty Athenian heavy infantry, not a man less, and all in the prime of life. These were by far the best men in the city of Athens that fell during this war. Among the slain was also Procles, the colleague of Demosthenes. Meanwhile the Athenians took up their dead under truce from the Aetolians, and retired to Naupactus, and from thence went in their ships to Athens; Demosthenes staying behind in Naupactus and in the neighbourhood, being afraid to face the Athenians after the disaster.

About the same time the Athenians on the coast of Sicily sailed to Locris, and in a descent which they made from the ships defeated the Locrians who came against them, and took a fort upon the river Halex.

The same summer the Aetolians, who before the Athenian expedition had sent an embassy to Corinth and Lacedaemon, composed of Tolophus, an Ophionian, Boriades, an Eurytanian, and Tisander, an Apodotian, obtained that an army should be sent them against Naupactus, which had invited the Athenian invasion. The Lacedaemonians accordingly sent off towards autumn three thousand heavy infantry of the allies, five hundred of whom were from Heraclea, the newly founded city in Trachis, under the command of Eurylochus, a Spartan, accompanied by Macarius and Menedaius, also Spartans.

The army having assembled at Delphi, Eurylochus sent a herald to the Ozolian Locrians; the road to Naupactus lying through their territory, and he having besides conceived the idea of detaching them from Athens. His chief abettors in Locris were the Amphissians, who were alarmed at the hostility of the Phocians. These first gave hostages themselves, and induced the rest to do the same for fear of the invading army; first, their neighbours the Myonians, who held the most difficult of the passes, and after them the Ipnians, Messapians, Tritaeans, Chalaeans, Tolophonians, Hessians, and Oeanthians, all of whom joined in the expedition; the Olpaeans contenting themselves with giving hostages, without accompanying the invasion; and the Hyaeans refusing to do either, until the capture of Polis, one of their villages.

His preparations completed, Eurylochus lodged the hostages in Kytinium, in Doris, and advanced upon Naupactus through the country of the Locrians, taking upon his way Oeneon and Eupalium, two of their towns that refused to join him. Arrived in the Naupactian territory, and having been now joined by the Aetolians, the army laid waste the land and took the suburb of the town, which was unfortified; and after this Molycrium also, a Corinthian colony subject to Athens. Meanwhile the Athenian Demosthenes, who since the affair in Aetolia had remained near Naupactus, having had notice of the army and fearing for the town, went and persuaded the Acarnanians, although not without difficulty because of his departure from Leucas, to go to the relief of Naupactus. They accordingly sent with him on board his ships a thousand heavy infantry, who threw themselves into the place and saved it; the extent of its wall and the small number of its defenders otherwise placing it in the greatest danger. Meanwhile Eurylochus and his companions, finding that this force had entered and that it was impossible to storm the town, withdrew, not to Peloponnese, but to the country once called Aeolis, and now Calydon and Pleuron, and to the places in that neighbourhood, and Proschium in Aetolia; the Ambraciots having come and urged them to combine with them in attacking Amphilochian Argos and the rest of Amphilochia and Acarnania; affirming that the conquest of these countries would bring all the continent into alliance with Lacedaemon. To this Eurylochus consented, and dismissing the Aetolians, now remained quiet with his army in those parts, until the time should come for the Ambraciots to take the field, and for him to join them before Argos.

Summer was now over. The winter ensuing, the Athenians in Sicily with their Hellenic allies, and such of the Sicel subjects or allies of Syracuse as had revolted from her and joined their army, marched against the Sicel town Inessa, the acropolis of which was held by the Syracusans, and after attacking it without being able to take it, retired. In the retreat, the allies retreating after the Athenians were attacked by the Syracusans from the fort, and a large part of their army routed with great slaughter. After this, Laches and the Athenians from the ships made some descents in Locris, and defeating the Locrians, who came against them with Proxenus, son of Capaton, upon the river Caicinus, took some arms and departed.

The same winter the Athenians purified Delos, in compliance, it appears, with a certain oracle. It had been purified before by Pisistratus the tyrant; not indeed the whole island, but as much of it as could be seen from the temple. All of it was, however, now purified in the following way. All the sepulchres of those that had died in Delos were taken up, and for the future it was commanded that no one should be allowed either to die or to give birth to a child in the island; but that they should be carried over to Rhenea, which is so near to Delos that Polycrates, tyrant of Samos, having added Rhenea to his other island conquests during his period of naval ascendancy, dedicated it to the Delian Apollo by binding it to Delos with a chain.

The Athenians, after the purification, celebrated, for the first time, the quinquennial festival of the Delian games. Once upon a time, indeed, there was a great assemblage of the Ionians and the neighbouring islanders at Delos, who used to come to the festival, as the Ionians now do to that of Ephesus, and athletic and poetical contests took place there, and the cities brought choirs of dancers. Nothing can be clearer on this point than the following verses of Homer, taken from a hymn to Apollo: