In recommending extraordinary efforts to create a navy as well as to acquire nautical practice, Themistoklês displayed all that sagacious appreciation of the circumstances and dangers of the time for which Thucydides gives him credit: and there can be no doubt that Aristeidês, though the honester politician of the two, was at this particular crisis the less essential to his country. Not only was there the struggle with Ægina, a maritime power equal or more than equal, and within sight of the Athenian harbor,—but there was also in the distance a still more formidable contingency to guard against. The Persian armament had been driven with disgrace from Attica back to Asia; but the Persian monarch still remained with undiminished means of aggression and increased thirst for revenge; and Themistoklês knew well that the danger from that quarter would recur greater than ever. He believed that it would recur again in the same way, by an expedition across the Ægean like that of Datis to Marathon;[87] against which the best defence would be found in a numerous and well-trained fleet. Nor could the large preparations of Darius for renewing the attack remain unknown to a vigilant observer, extending as they did over so many Greeks subject to the Persian empire. Such positive warning was more than enough to stimulate the active genius of Themistoklês, who now prevailed upon his countrymen to begin with energy the work of maritime preparation, as well against Ægina as against Persia.[88] Not only were two hundred new ships built, and citizens trained as seamen,—but the important work was commenced, during the year when Themistoklês was either archon or general, of forming and fortifying a new harbor for Athens at Peiræus, instead of the ancient open bay of Phalêrum. The latter was indeed somewhat nearer to the city, but Peiræus, with its three separate natural ports,[89] admitting of being closed and fortified, was incomparably superior in safety as well as in convenience. It is not too much to say, with Herodotus,—that the Æginetan “war was the salvation of Greece, by constraining the Athenians to make themselves a maritime power.”[90] The whole efficiency of the resistance subsequently made to Xerxes turned upon this new movement in the organization of Athens, allowed as it was to attain tolerable completeness through a fortunate concurrence of accidents; for the important delay of ten years, between the defeat of Marathon and the fresh invasion by which it was to be avenged, was in truth the result of accident. First, the revolt of Egypt; next, the death of Darius; thirdly, the indifference of Xerxes, at his first accession, towards Hellenic matters,—postponed until 480 B. C., an invasion which would naturally have been undertaken in 487 or 486 B. C., and which would have found Athens at that time without her wooden walls,—the great engine of her subsequent salvation.