At Susa Alexander received reinforcements of about 15,000 men from Greece. He then directed his march south-eastwards towards Persepolis. His road lay through the mountainous territory of the Uxians, who refused him a passage unless he paid the usual tribute which they were in the habit of extorting even from the Persian kings. But Alexander routed them with great slaughter. He then advanced rapidly to Persepolis, whose magnificent ruins still attest its ancient splendour. It was the real capital of the Persian kings, though they generally resided at Susa during the winter, and at Ecbatana in summer. The treasure found there exceeded that both of Babylon and Susa, and is said to have amounted to 120,000 talents or nearly 30,000,000l. sterling. It was here that Alexander is related to have committed an act of senseless folly, by firing with his own hand the ancient and magnificent palace of the Persian kings; of which the most charitable version is that he committed the act when heated with wine at the instigation of Thais, an Athenian courtezan. By some writers, however, the story is altogether disbelieved, and the real destruction of Persepolis referred to the Mahommedan epoch. Whilst at Persepolis, Alexander visited the tomb of Cyrus, the founder of the Persian monarchy, which was situated at a little distance, at a city called Pasargadae.

Thus in between three and four years after crossing the Hellespont Alexander had established himself on the Persian throne. But Darius was not yet in his power. After the battle of Arbela that monarch had fled to Ecbatana. It was not till about four months after the battle of Arbela, and consequently early in 330, that Alexander quitted Persepolis to resume the pursuit of Darius. On approaching Ecbatana he learned that the Persian monarch had already fled with the little army which still adhered to him. Alexander, with his main body, then pursued Darius through Media by forced marches and reached Rhagae, a distance of three hundred miles from Ecbatana, in eleven days. Such was the rapidity of the march that many men and horses died of fatigue. At Rhagae he heard that Darius had already passed the defile called the "Caspian Gates," leading into the Bactrian provinces; and, as that pass was fifty miles distant, urgent pursuit was evidently useless. He therefore allowed his troops five days' rest, and then resumed his march. Soon after passing the Gates he learned that Darius had been seized and loaded with chains by his own satrap Bessus, who entertained the design of establishing himself in Bactria as an independent sovereign. This intelligence stimulated Alexander to make still further haste with part of his cavalry and a chosen body of foot. On the fourth day he succeeded in overtaking the fugitives with his cavalry, having been obliged to leave the infantry behind, with directions to follow more at leisure. The enemy, who did not know his real strength, were struck with consternation at his appearance, and fled precipitately. Bessus and his adherents now endeavoured to persuade Darius to fly with them, and provided a fleet horse for that purpose. But the Persian monarch, who had already experienced the generosity of Alexander in the treatment of his captive family, preferred to fall into his hands, whereupon the conspirators mortally wounded him in the chariot in which they kept him confined, and then took to flight. Darius expired before Alexander could come up, who threw his own cloak over the body. He then ordered him to be magnificently buried in the tomb of his ancestors, and provided for the fitting education of his children.

The next three years were employed by Alexander in subduing Hyrcania, Drangiana, Bactria, and Sogdiana, and the other northern provinces of the Persian empire. In these distant regions he founded several cities, one of which in Aria, called after him (Alexandria Ariorum), is still, under the name of HERAT, one of the chief cities in central Asia. Alexander's stay in Prophthasia, the capital of Drangiana, was signalized by a supposed conspiracy against his life, formed by Philotas, the son of Parmenio. Alexander had long entertained suspicions of Philotas. But the immediate subject of accusation against him was that he had not revealed a conspiracy which was reported to be forming against Alexander's life, and which he had deemed too contemptible to notice. He was consequently suspected of being implicated in it; and on being put to the torture he not only confessed his own guilt in his agonies, but also implicated his father. Philotas was executed, and an order was sent to Ecbatana, where Parmenio then was, directing that veteran general to be put to death. A letter, purporting to be from his son, was handed to him; and whilst the old man was engaged in reading it, Polydamus, his intimate friend, together with some others of Alexander's principal officers, fell upon and slew him. His head was carried to Alexander.

Meantime Bessus had assumed the royal dignity in Bactria; but upon Alexander's approach he fled across the Oxus into Sogdiana. Early in the summer of 329 Alexander followed him across the Oxus; and shortly afterwards Bessus was betrayed by two of his own officers into the hands of Alexander. Bessus was carried to Zariaspa, the capital of Bactria, where he was brought before a Persian court, and put to death in a cruel and barbarous manner.