A far worse result of the Cyreian expedition was the revelation which it made of the weakness of Persia, and of the facility with which a Greek force might penetrate to the very midst of the Empire, defeat the largest army that could be brought against it, and remain, or return, as it might think proper.
Hitherto Babylon and Susa had been, even to the mind of a Greek statesman, remote localities, which it would be the extreme of rashness to attempt to reach by force of arms, and from which it would be utter folly to suppose that a single man could return alive except by permission of the Great King.

Henceforth these towns were looked upon as prizes quite within the legitimate scope of Greek ambition, and their conquest came to be viewed as little more than a question of time.

The opinion of inaccessibility, which had been Persia's safeguard hitherto, was gone, and in its stead grew up a conviction that the heart of the Empire might be reached with very little difficulty.
It required, however, for the production of this whole change, not merely that the advance to Cunaxa should have been safely made, and the immeasurable superiority of Greek to Asiatic soldiers there exhibited, but also that the retreat should have been effected, as it was effected, without disaster.

Had the Ten Thousand perished under the attacks of the Persian horse, or even under the weapons of the Kurds, or amid the snows of Armenia, the opinion of Persian invulnerability would have been strengthened rather than weakened by the expedition.

But the return to Greece of ten thousand men, who had defeated the hosts of the Great King in the centre of his dominions, and fought their way back to the sea without suffering more than the common casualties of war, was an evidence of weakness which could not but become generally known, and of which all could feel the force.