Thucydides, History of the Peloponnesian War
Benjamin Jowett, Ed.

8. On the return of the Peloponnesians from Attica, the Spartans and the Perioeci¹ in the² neighbourhood of the city³ went at once to attack Pylos, but the other Lacedaemonians, having only just returned from an expedition, were slower in arriving. [2] A message was sent round the Peloponnesus bidding the allies come without a moment's delay and meet at Pylos; another message summoned the sixty Peloponnesian ships from Corcyra. These were carried over the Leucadian isthmus⁴, and, undiscovered by the Athenian ships, which were by this time at Zacynthus, reached Pylos, where their land forces had already assembled. [3] While the Peloponnesian fleet was still on its way, Demosthenes succeeded in despatching unobserved two vessels to let Eurymedon and the Athenian fleet know of his danger, and to bid them come at once. [4] While the Athenian ships were hastening to the assistance of Demosthenes in accordance⁵ with his request, the Lacedaemonians prepared to attack the fort both by sea and by land; they thought that there would be little difficulty in taking a work hastily constructed and defended by a handful of men. [5] But as they expected the speedy arrival of the Athenian fleet they meant to close the entrances to the harbour, and prevent the Athenians from anchoring there should they fail in taking the fort before their arrival.

The island which is called Sphacteria stretches along the land and is quite close to it, making⁶ the harbour safe and the entrances narrow; [6] there is only a passage for two ships at the one end, which was opposite Pylos and the Athenian fort, while at the other the strait between the island and the mainland⁷ is wide enough to admit eight or nine. The length of the island is about a mile and threequarters; it was wooded, and being uninhabited had no roads. The Lacedaemonians were intending to block up the mouths of the harbour by ships placed close together with their prows outwards; [7] meanwhile, fearing lest the Athenians should use the island for military operations, they conveyed thither some hoplites, and posted others along the shore of the mainland. Thus both the island and the mainland would be hostile to the Athenians; [8] and nowhere on the mainland would there be a possibility of landing. For on the shore of Pylos itself, outside the entrance of the strait, and where the land faced the open sea, there were no harbours, and the Athenians would find no position from which they could assist their countrymen. Meanwhile the Lacedaemonians, avoiding the risk of an engagement at sea, might take the fort, which had been occupied in a hurry and was not provisioned. [9] Acting on this impression they conveyed their hoplites over to the island, selecting them by lot out of each division of the army. One detachment relieved another; those who went over last and were taken in the island were four hundred and twenty men, besides the Helots who attended them; they were under the command of Epitadas the son of Molobrus.