The assistance which Cyrus had rendered to the Lacedaemonians in the Peloponnesian war led to a remarkable episode in Grecian history. This was the celebrated expedition of Cyrus against his brother Artaxerxes, in which the superiority of Grecian to Asiatic soldiers was so strikingly shown.

The death of Darius Nothus, king of Persia, took place B.C. 404, shortly before the battle of AEgospotami. Cyrus, who was present at his father's death, was charged by Tissaphernes with plotting against his elder brother Artaxerxes, who succeeded to the throne. The accusation was believed by Artaxerxes, who seized his brother, and would have put him to death, but for the intercession of their mother, Parysatis, who persuaded him not only to spare Cyrus but to confirm him in his former government. Cyrus returned to Sardis burning with revenge, and fully resolved to make an effort to dethrone his brother.

From his intercourse with the Greeks Cyrus had become aware of their superiority to the Asiatics, and of their usefulness in such an enterprise as he now contemplated. The peace which followed the capture of Athens seemed favourable to his projects. Many Greeks, bred up in the practice of war during the long struggle between that city and Sparta, were now deprived of their employment, whilst many more had been driven into exile by the establishment of the Spartan oligarchies in the various conquered cities. Under the pretence of a private war with the satrap, Tissaphernes, Cyrus enlisted large numbers of them in his service. The Greek in whom he placed most confidence was Clearchus, a Lacedaemonian, and formerly harmost of Byzantium, who had been condemned to death by the Spartan authorities for disobedience to their orders.

It was not, however, till the beginning of the year B.C. 401 that the enterprise of Cyrus was ripe for execution. The Greek levies were then withdrawn from the various towns in which they were distributed, and concentrated in Sardis, to the number of about 8000; and in March or April of this year Cyrus marched from Sardis with them, and with an army of 100,000 Asiatics. The object of the expedition was proclaimed to be an attack upon the mountain-freebooters of Pisidia; its real destination was a secret to every one except Cyrus himself and Clearchus. Among the Greek soldiers was Xenophon, an Athenian knight, to whom we owe a narrative of the expedition. He went as a volunteer, at the invitation of his friend Proxenus, a Boeotian, and one of the generals of Cyrus.

The march of Cyrus was directed through Lydia and Phrygia. after passing Colossae he arrived at Colaenae, where he was joined by more Greek troops, the number of whom now amounted to 11,000 hoplites and 2000 peltasts. The line of march, which had been hitherto straight upon Pisidia, was now directed northwards. Cyrus passed in succession the Phrygian towns of Peltae, Ceramon Agora, the Plain of Cayster, Thymbrium, Tyriaeum, and Iconium, the last city in Phrygia. Thence he proceeded through Lycaonia to Dana, and across Mount Taurus into Cilicia.

On arriving at Tarsus, a city on the coast of Cilicia, the Greeks plainly saw that they had been deceived, and that the expedition was designed against the Persian king. Seized with alarm at the prospect of so long a march, they sent a deputation to Cyrus to ask him what his real intentions were. Cyrus replied that his design was to march against his enemy, Abrocomas, satrap of Syria, who was encamped on the banks of the Euphrates. The Greeks, though they still suspected a delusion, contented themselves with this answer in the face of their present difficulties, especially as Cyrus promised to raise their pay from one Daric to one Daric and a half a month. The whole army then marched forwards to Issus, the last town in Cilicia, seated on the gulf of the same name. Here they met the fleet, which brought them a reinforcement of 1100 Greek soldiers, thus raising the Grecian force to about 14,000 men.

Abrocomas, who commanded for the Great King in Syria and Phoenicia, alarmed at the rapid progress of Cyrus, fled before him with all his army, reported as 300,000 strong; abandoning the impregnable pass situated one day's march from Issus, and known as the Gates of Cilicia and Syria. Marching in safety through this pass, the army next reached Myriandrus, a seaport of Phoenicia. From this place Cyrus struck off into the interior, over Mount Amanus. Twelve days' march brought him to Thapsacus on the Euphrates, where for the first time he formally notified to the army that he was marching to Babylon against his brother Artaxerxes, The water happened to be very low, scarcely reaching to the breast; and Abrocomas made no attempt to dispute the passage. The army now entered upon the desert, where the Greeks were struck with the novel sights which met their view, and at once amused and exhausted themselves in the chase of the wild ass and the antelope, or in the vain pursuit of the scudding ostrich. After several days of toilsome march the army at length reached Pylae, the entrance into the cultivated plains of Babylonia, where they halted a few days to refresh themselves.