Before we proceed with the history of the period which followed the close of the Peloponnesian war, our attention must for a time be turned to a series of events, which, though they took place for the most part far beyond the limits of Greece, and did not immediately affect its interests, will be found to be most intimately connected with its final destinies, and with some of the greatest revolutions of the ancient civilised world; and, in the brief account which we are about to give of them, we shall be chiefly guided by this view of their relative importance.

They arose out of the ambition of Cyrus, of whose abilities and enterprising spirit some specimens have been already seen, and were the results of an attempt which he made to place himself on the throne of Persia. He was the second of the four sons of Darius and Parysatis, and, according to the customs of the monarchy, his elder brother Artaxerxes was the legitimate heir apparent. But Cyrus was the first son born to Darius after his accession to the throne, and he was his mother's favourite. She had encouraged him to hope that as Xerxes, through the influence of Atossa, had been preferred to his elder brother who was born while their father was yet in a private station, so she should be able to persuade Darius to set aside Artaxerxes, and declare Cyrus his successor.

While these movements were taking place in Greece, Agesilaus was carrying on the war in Asia, with an activity and success which might well have alarmed the Persian court, and proved the wisdom of the precautions adopted by Tithraustes. On his march into the province of Pharnabazus, he was accompanied by Spithridates, who urged him to advance into Paphlagonia, and undertook to make Cotys, the king of that country, his ally. Cotys, who is elsewhere named Corylas, was one of those powerful hereditary vassals of the Persian king, whose subjection had become merely nominal, and he had lately renounced even the appearance of submission. Artaxerxes, imprudently or insidiously, had put his obedience to the test, by summoning or inviting him to court. But the Paphlagonian prince was too wary, and knew the character of the Persian government too well, to trust himself in its power, and he had openly refused to obey the royal command. It would add nothing to his offence, though something to his security, to treat with the enemies of Artaxerxes. Nothing could be more agreeable to Agesilaus than the opportunity of gaining so powerful an ally; he gladly accepted the mediation of Spithridates, who not only fulfilled his promise, and engaged Cotys to come to the Greek camp, and conclude an alliance with Sparta in person, but prevailed on him, before his departure, to leave a reinforcement of 1000 cavalry, and 2000 targeteers, with the army of Agesilaus.

Within a few days after the battle of Salamis Attica was delivered from the presence of the barbarians, and the Athenians returned to cultivate their fields and to repair their dwellings. The necessity of attending to their domestic concerns had been one of the main arguments by which Themistocles prevailed on them to desist from the pursuit of the Persian fleet. They now applied themselves to their useful labours with the greater alacrity, as they entertained a reasonable hope that their land would not again be visited by the ravages of the same invader. Sparta had been too late for Marathon, too late to save Athens; but now there was ample time for preparation, and full warning of the need. Though the enemy was yet formidable by land, still after the brilliant success that had hitherto attended the Greeks, after the example that had been given at Marathon, of what might be effected by a small number of brave and disciplined troops, it was not too much to expect that the allies would not again look on at a distance, while the barbarians overran the territory of a people which had done and suffered so much for the common cause. During the winter the Greeks remained tranquil, as if they had no enemy at their doors: but in the spring they awoke, like men who have slept upon an uneasy thought, and remembered that Mardonius was in Thessaly, and a Persian fleet still upon the sea.

Darius Hystaspis was not a conqueror like Cyrus or Cambyses: the ruling maxim of his government seems to have been to aim rather at consolidating and securing his empire than at enlarging it; and though he was engaged in wars almost throughout his whole reign, they all partook of a defensive character, and were the result of prudence, or necessity, or chance, rather than of deliberate ambition. Hence it arose that his attention was chiefly turned toward the western side of his dominions, where accidental causes brought him into collision with the Greeks, and produced those memorable events which we are now about to relate. Had his genius resembled that of his predecessors he would probably have directed his views toward the East, where the kingdoms of India lay open to his arms. On this side the Indus appears to have been the boundary of his empire, and the Indians who composed the twentieth satrapy, and whose tribute according to Herodotus exceeded a third of that of all the remainder, were probably the inhabitants of the modern Candahar, and Cabul, and the adjacent lands west of the Indus. Of the vast and rich country beyond he knew only by report, which however had undoubtedly spread the fame of its wonderful fertility and opulence: but though he employed a Greek navigator, Scylax of Caryanda, to follow the Indus into the ocean, and to survey the coast from its mouth westward, he does not seem to have formed any settled design of conquest in this quarter.

The ravages of the pestilence continued in Attica for two years without any abatement; and in the fourth summer of the war, 428, the country was again invaded by a Peloponnesian army under the command of king Archidamus. The policy which prudence had dictated to Pericles was maintained after his death, partly perhaps through the weakness and depression caused by the sickness, and partly because the enemy's presence had now become more familiar, and no longer excited the same emotions. The Athenians contented themselves with annoying the enemy, as opportunity offered itself, with their cavalry, which prevented his light troops from spreading over the country, and infesting the immediate neighbourhood of the city, and forced them to keep within the shelter of the heavy infantry. At the same time they equipped a fleet of forty galleys, which prepared to sail round Peloponnesus, under the command of Cleippides and two colleagues.

But in the mean while they were threatened in a distant quarter with a blow, which, if it had taken effect, not only would have immediately weakened their power, but might have proved ruinous in its remote consequences. We have already mentioned, that before the war broke out Mitylene had only been prevented from casting off the Athenian yoke by the reluctance which the Spartans felt to break the Thirty Years' Truce.