Darius I, fourth of the Achæmenian dynasty, founded Persepolis, about forty miles northeast of the modern Shiraz, commenced building the famous palace and constructed for himself a tomb. Xerxes I added a palace and a tomb of his own, while tombs also were built by Artaxerxes III and Darius II. But, while Persepolis remained the favourite resort of the Persian Kings, it was too remote a spot to be the seat of government, which continued to be divided between Babylon, Susa, and Ecbatana. Meanwhile, under Xerxes I the Persian power came into conflict with the Hellenic and was worsted in the battles of Platæa and Thermopylæ and the sea-fight at Salamis. Henceforth the advance of the Persian Empire was checked; dissensions began to weaken it; the central authority relapsed into feebleness, with lurid intervals of cruelty, until finally it succumbed to the rising tide of Macedonian conquest. In 331 <small>B.C.</small> Alexander the Great crushed the army of Darius III near Arbela; took in turn the cities of Babylon, Susa, and Ecbatana and stripped them of their treasure, finally capturing Persepolis, and setting fire to it. This act of vandalism has been variously explained. One story, which forms the subject of Dryden’s “Ode to Saint Cecilia’s Day,” had it that the wanton act was instigated by the courtezan, Thais. Another story is that it was an act of revenge for the destruction of Greek temples by Xerxes I; while still another relates that in this destruction of the very heart of Iran, Alexander wished to impress the Oriental imagination with the absoluteness of his supremacy. After being subject to the rule of the successors of Alexander and to the domination of the later Parthian Empire, Persia once more became an empire under the Sassanian Dynasty, Ctesiphon being one of its chief cities. In the seventh century <small>A.D.</small> it was conquered by the Saracens and entered into the Mohammedan civilisation, which we shall discuss in a later chapter. * * * * * The rapid rise of the Persian power was due to the hardiness of this mountain race and its highly organised preparation for war. Every Persian able to bear arms was bound to serve the King: the great landowners on horseback, the commonalty on foot. The army, therefore, unlike those of the Oriental nations it encountered, was composed of cavalry as well as infantry; and, while the latter, armed with bows, kept the enemy at a distance and harassed them with storms of arrows, the cavalry, operating on their flanks and rear, completed the rout. It was only when the power had become unwieldy by its very vastness, that this method of warfare proved useless against the Greek hoplites and the massed formation of the Macedonian phalanx.