Fortune favoured his design. For on rounding the western headland of Peloponnesus, the fleet encountered a storm, and was compelled to seek shelter at Pylos. Demosthenes now urged the admirals to employ their enforced leisure in fortifying the place. But they repulsed him rudely, and treated his suggestion with contempt. He next tried to interest the inferior officers in his project, but meeting with no better success, he began to fear that this grand opportunity would be thrown away. The discussion, however, had reached the ears of the soldiers, and having nothing else to do, they agreed among themselves to pass the time by building a fort. Choosing a place of great natural strength, where the rocky coast descends abruptly to the open sea, they went to work with a will. As they had no tools for stone-cutting, they picked out the stones, and fitted them together according to their shape; and for want of hods they carried the mortar, wherever it was required, on their backs, stooping forward and clasping their hands together behind them, to prevent it from slipping off. They carried out their self-imposed task with great energy, and after six days of vigorous labour the fort was completed, for the natural defences of the site were so strong that in most places there was no need of a wall. As the weather was now favourable, the fleet proceeded on its voyage, leaving Demosthenes with five ships to garrison the fort.

The news of the occupation of Pylos soon reached the Spartans, but at first they paid little heed, thinking that they could expel the audacious intruders whenever they chose to exert themselves. Moreover, they were just then engaged in keeping one of those religious festivals of which the Spartan calendar was so full, and a good part of their army was absent in Attica. Agis, however, the Spartan king, and those under him who were commanding in Attica, took a wiser view of the situation, and cutting short their operations they led their forces with all speed back to Sparta. They were the more inclined to do this as the season was yet early, the weather inclement, and, the corn being still green, they wanted means to nourish their troops. Thus the inventive genius of Demosthenes had already proved of signal service to his country; for this was the shortest of all the Peloponnesian invasions, lasting only fifteen days.

On the return of their troops from Attica the Spartans sent a small force to commence the attack on Pylos, and ordered the main body of their army to follow. There was some discontent among those who had already been serving abroad at this second levy, and the full muster of the troops was consequently delayed. In the meantime a message was despatched to a Peloponnesian fleet then sailing to Corcyra, which at this time was in a state of revolution, with orders to return at once, and assist in the campaign against Pylos. Demosthenes was now in imminent danger, being threatened with an immediate assault by sea and land, which he had no adequate means of repelling. Having sent off two of his ships to recall the Athenian squadron from its voyage to Corcyra, he prepared to defend himself, until the arrival of succour, as best he could.

The Peloponnesian fleet was the first to arrive, and the Spartans, who were now present in full force with their allies, determined to make the most of their time. They hoped, by a simultaneous onslaught of their army and fleet, to carry the fort before the Athenian ships had time to return. But in case they should fail in this, they intended to cripple the movements of the relieving squadron, by blocking the entrances to the bay. For the long, narrow island of Sphacteria forms a natural break water, converting the harbour of Navarino into a land-locked basin, with two narrow passages at the northern and southern end. [Footnote: The description of Thucydides does not correspond to the picture of the harbour given in our modern maps. But in the course of twenty centuries great changes may well have occurred.] These inlets the Spartans proposed to close, by anchoring triremes close together, with their prows turned seawards, which they could easily have done, for at the southern entrance there was only room for eight or nine vessels to sail abreast, and at the northern entrance only room for two. This precaution, however, was never carried out; and the Spartans, as if blinded by fate, adopted another measure, which led to fatal consequences for themselves. Wishing to keep command of every spot of land in the neighbourhood of Pylos, they landed a body of their own men, numbering four hundred and twenty, with the usual proportion of Helots, on the island, and the same time posted troops at every assailable point on the opposite coast.

Thinking now that the little garrison at Pylos, surrounded on all sides by enemies, would fall an easy prey, they sent orders to the fleet to get under way, and prepared to attack the fort on the land side. Meanwhile Demosthenes had not been idle: having drawn his three remaining ships under the shelter of the fort, and protected them in front by a stockade, he armed the crews with such weapons as he had, including a number of wicker-shields, taken from a thirty-oared Messenian galley which had recently come to his assistance with a force of forty hoplites. Then, having posted the greater part of his troops for the defence of his position against the Peloponnesian army, he himself descended with a picked body of sixty hoplites, and took up his station on the rocky shore. For on this side the defences were weakest, as the Athenians, in building the fort, had never anticipated an attack from the sea.

Demosthenes had just time to address a few words of caution and encouragement to his men, assuring them of victory, if they would only stand fast, when the Peloponnesian fleet was seen bearing down upon them; and at the same moment a loud shout from the fort announced that the garrison was already engaged behind them. The assault was fiercest at the point where Demosthenes and his men were stationed, and the Peloponnesians made desperate efforts to effect a landing. But they were embarrassed by the difficult and rocky coast, which only allowed a few ships to approach at a time. As fast as one division was beaten back, another came on, with the white foam spouting round the prows, and the waters roaring and eddying to the strokes of the gigantic oars, while the cliffs resounded with the shouts of their comrades in the ships behind, cheering them on to the attack.

Conspicuous among those who fought on the ships was seen the gallant figure of Brasidas, who exerted himself, by voice and by example, to infuse his own heroic spirit into the rest of the crews and their officers. His ringing tones were heard above the tumult, urging on the captains and steersmen, when they hung back in fear lest their ships should be shattered on the rocks. "Spare not these timbers," he cried, "but let every hull among them go to wreck, rather than suffer the enemy to violate the soil of Lacedaemon. Where is your loyalty to Sparta? Have you forgotten the debt which you owe to her? Have at them, I say, and hurl this fort with its defenders into the sea." Saying this he ordered the master of his own trireme to beach the vessel, and stood ready on the gangway, that he might be the first to leap on shore. But as he attempted to land he was hurled back by the Athenians, and fell fainting, covered with wounds, on the deck. His shield slipped off his arm, and dropped into the sea, and having been washed ashore, was picked up by the Athenians, who used it to adorn the trophy which they afterwards erected.

After the fall of Brasidas the Peloponnesians still continued their efforts to effect a landing, but they were baffled by the obstinate defence of the Athenians, and the rugged and inhospitable coast. It was a strange reversal of affairs which had been brought about by the fortune of war. On one side were the Spartans, trained to military service on land, but now compelled to serve on board a fleet, in order to obtain a footing on their own territory, and on the other side the Athenians, whose natural element was the sea, drawn up on land to repel a naval attack.

Next day the assault was repeated, but again without success. The Spartans sent for a supply of timber, to construct siege engines, intending to try and batter down the Athenian wall where it overlooked the harbour, as at this point there was a better landing-place for the ships. In this task, however, they were interrupted by the sudden appearance of the Athenian fleet, now numbering fifty vessels, having been reinforced by four Chian ships, and six from Naupactus. Finding the harbour occupied by the Peloponnesians, and the whole coast lined with troops, they retired for the night to the little island of Prote. Next day they weighed anchor early, and dividing their fleet, sailed into the harbour of Navarino by both entrances at once. Though taken by surprise, the Peloponnesians manned their ships, and as fast as they were ready put out to meet them; but before their array was complete they were attacked by the Athenians, who disabled many of their vessels, captured five, and drove the rest ashore. So complete was the rout that the Athenians pursued the flying ships into the very interior of the harbour, and rammed some of them after they had been brought to land. Others they charged while the crews were still getting on board, and began to tow off the disabled hulls. But in the heat of victory the Athenians had pushed their advantage somewhat too far, and they paid for their audacity by the loss of a considerable number of their men. For the Lacedaemonians, in wild dismay at the defeat of their ships, by which their comrades on the island would be cut off from all help, made desperate exertions to save their fleet, wading into the water in their heavy armour, and hauling back the vessels as they were being towed off. In the confined space manoeuvring was impossible, and the sea-fight had now become a furious hand to hand encounter, as between two armies on land. After a prolonged struggle, in which both sides suffered severely, the Spartans succeeded in saving their ships, except those which had been taken at first, and the Athenians then retired to their station.

The result of this battle was to give the Athenians complete command of the sea, for the Peloponnesian fleet was in no condition to renew the engagement. From their camp on the mainland the Spartans could see the Athenian triremes rowing round and round the island, and keeping vigilant watch, to prevent those who were confined there from escaping. News of the disaster was sent without delay to Sparta, and the magistrates, recognising the gravity of the crisis, proceeded at once to Pylos, wishing to inform themselves on the spot, and then decide what was best to be done. Finding on their arrival that there was no prospect of rescuing their men on the island, they applied to the Athenian commanders for a truce, to enable them to send envoys to Athens, and arrange some terms for the recovery of the imprisoned Spartans. The Athenians consented, and a truce was made on the following conditions: The Spartans were to surrender all their fleet, including any ships of war on the coast of Laconia, to the Athenians, and to refrain from any attack on the fort, until the return of the envoys. The Athenians, on their part, agreed to allow provisions to be sent to the Spartans on the island, all such provision being conveyed thither under their own inspection, and none by stealth. They further agreed to carry the envoys to Athens in one of their own triremes, and to suspend all hostilities until the expiration of the truce. When the envoys returned, the Peloponnesian ships were to be given back.