He went to work slowly, for the task was great; and it was all to do, since Datis and Artaphernes had failed to establish a footing on the western mainland. Moreover, that expedition had shown him the difficulty, if not the impossibility of isolating the immediate object of attack. Pan-Hellenic sentiment may not at the time have been stronger west than east of the Ægean; but its practical expression, in the form of combination among the states, was infinitely easier on the European than on the Asiatic side. The years of the revolt had furnished him with all the data for an estimate of the formidable character of this sentimental factor in the politics of this western border of his empire. The punishment of the free Ionians, and the establishment of a _tête-du-pont_ on the European shore, could only be accomplished by a force sufficiently large to meet a formidable combination among the Greek states. In the years following Marathon,—the last years of his eventful life,—he set to work to prepare for the great expedition. The work was necessarily a work of time. Apart from the magnitude of the undertaking, the last ten years must have severely strained even the great resources of his empire. Moreover, those resources were, owing to the methods on which the government of the empire was organised, potential rather than active. Persia possessed the materials for a great army; but she did not keep that army in commission. Prompt action was impossible with her when the action was to be on a large scale. Some years passed, and yet the blow did not fall on Greece. The exhausted state of the empire, apart from the habitual slowness in the working of its military machinery, must have delayed the progress of the preparations. ◆H. vii. 2.◆ Darius, too, was in the decline of his days; and it may well be that a failure in his health, apparent some years before his actual death, led to those quarrels about the succession, the story of which reached Greece, and is reproduced by Herodotus, after his custom, with much circumstantial detail. This failure of energy at the centre of the empire would entail a corresponding lack of energy in the outlying parts of it. #DEATH OF DARIUS.# Whatever the progress made in the years immediately succeeding Marathon,[87] an event took place in 486 which diverted the attention of Darius to another part of the world. Egypt revolted. But the old king was dying; and before the work of suppressing the revolt was carried out, he passed away in 485. Enough has been said about him in connection with his organization of the empire to make it unnecessary to write his obituary here. Singularly able, singularly enlightened, and, for the time in which he lived, singularly humane, he stands forth in history as the greatest Oriental that ever ruled in Western Asia. In the year after Darius died the revolt in Egypt was suppressed.