Geography may help to explain the Great King's priorities, for Iran and the 'upper satrapies' east of the river Tigris were a land of two main landscapes, neither of them suited to the passage of great armies. There was the boundless prospect of the desert steppes in the centre and the north of the empire where men strayed no faster than their flocks and the only rapid movement was the post haste of the courier and the king's work-parties down the stageposts of the rough Royal Road. Food was confined to a few oases of the water which Iranians always worshipped. If a man strayed into the desert he would not go far without the help of the Bactrian camel, hardy in mountain winters no less than in summer heat. 'When a desert wind is brewing, only the old camels have advance knowledge', wrote a Chinese traveller who had seen them, 'at once they stand in a group and snarl and bury their mouths in the sand. The men too cover their noses and mouths in felt and though the wind moves swiftly past, they would meet their deaths if they did not take this precaution.' The desert was not an enviable field for close administration, but it was at least more accessible than the mountains which ringed it round.

To the west, the Zagros mountains, to the east the Hindu Kush, to the north the impenetrable forests of Gurgan and the Elburz range, to the south the fastnesses of Persia itself, a province which Artaxerxes III, contemporary of Philip, had never visited during his reign: these ranges were the lair of cave dwellers and mountain shepherds, forest tribes and nomads where an army had to cut a path if it was to progress at all and where snow and mud kept its season unusually short. On the outskirts of the Persian palaces a traveller would meet with nomads whom the king, left alone in return for a safe passage through their routes of migration older and more basic than any centralized empire. The hill tribes too were left free and now had less of a grievance against their rulers; the Persians' empire spread like a ground mist through the plains and valleys and when it came up against a mountain it could only halt and state its own powers all the more firmly at the mountain's foot. It was not the least of the powerful claims of Persepolis, ritual centre of the empire, that it stood in a plain ringed round with chains of mountains which the king could never have controlled.

For this empire's survival, the kings relied on such bold and uncompromising statements of their power: they were far more easily made in the western empire. The Royal Road was smoother and faster; there was no Hindu Kush or unavoidable desert blocking authority's few routes. Politically, the difference was summed up in the different systems of water, the heart of Asian life. In upper Iran, the ingenious 'water-mines', or underground qanats fed local villages and rested in the local nobility's control. Power, like the water, was dispersed through these aristocracies, and the King's grasp was loose. But in the west, in Babylonia, water was centralized in the long royal canals. Officials held the centre, and multiplied: judges and inquisitors were attached to provincial garrisons and satraps' courts in order to enforce the King's Law in public disputes, taking priority over the law codes of their subjects. The King's bureaucracy worked in written languages which illiterate Iranians could not read; evidence of its detail is still being recovered and although its documents do not extend within seventy years of Alexander's march, it can no longer be underestimated. The precise taxing of the king's colonists, the hearing of appeals in the satrap's court, the uniform system of weights and measures, the elaborate documents for travellers on the Royal Road who deserved daily rations from its regular points of supply, these hints of an intricate government raise questions of interpreters, scribes and civil servants which only new clay tablets and Egyptian papyri will allow to be filled in. In the absence of detailed evidence it would be wrong to write off a bureaucracy which on a point of principle sent half as many rations to mothers of a new born daughter in their king's work-forces as to mothers of a new born son and which balanced the number of women in each local task force exactly to the number of men.

Despite the scribes and law codes, power at the Persian court was personal, depending on access to the king. The politics of Persia were the politics of the palace gate and usher, the cup bearer, eunuch and brides of the royal harem: just as the king received his power by the grace of the good god Ahura Mazda, so the courtier received his rank from the hand of the king, being set apart by the honour of a purple cloak, a golden brooch or necklace or the right to kiss the king on the cheek or see him face to face. In Persia too, the old court titles had been widened to new faces; the Honoured Equals had become a whole squadron in the army and few Royal Relations still had a claim to kinship with the king; there were the same banquets as at Pella, whose expense was minutely observed and whose occasions brought the king and his advisers into daily contact. 'And the king made a feast unto all the people that were present in Shushan, the palace, both unto great and small, seven days in the court of the garden of the king's palace, where there were white, green and blue hangings, fastened with cords of fine linen and purple to silver rings and pillars of marble; the beds were of gold and silver upon a pavement of red and blue, and white and black marble.' There is no more vivid evocation of the workings of the Persian court than the historical fiction of the Bible's Book of Esther.

At this court the king was a figure of superhuman majesty, of a sanctity which derived from his position and did not depend on the force of his achievements. Little is known of Alexander's opponent Darius III, but it is suggestive. His father and mother were brother and sister, and Darius too married his sister as a second wife. This incest may have become a necessary symbol for the Persian royal family, emphasising their superiority to an ordinary family's taboos. Its mental effects are still uncertain. Darius was handsome, at least, and was brave by repute, for he was said to have distinguished himself in single combat against the most seditious tribe in central Iran. Naturally, there were Greeks who slandered this inbred king as the son of a slave, or as a former courier on the Royal Road; in fact, his uncle was descended from a branch of the royal family and he had made his name as satrap of mountainous Armenia. Perhaps it was during this office that he married his first wife from neighbouring Cappadocia; it is

noticeable how this wild tribal kingdom, so often rebellious, would fight for his cause repeatedly and become the refuge for noble Iranian refugees during Alexander's conquests and the age of the Successors. From this little regarded satrapy, Darius had progressed through poisonings to the throne. His friend the Vizier Bagoas had the influence and the severity to make or destroy a king, and it was with his help that Darius had removed his family rivals and taken the kingdom in default of other royal adults. The young son of the great Artaxerxes III was still alive, and there may have been Persians who would have preferred him to a Darius of such distant royal blood. No judgement can be passed on Darius's abilities, because there is no solid evidence; it is likely, however, that the manner of his accession had helped to scatter the court and weaken the loyalties of several provincial governors. It was not for nothing that Alexander proclaimed him publicly a mere usurper.

Recent rebellion in western Asia and this royal intrigue at the Persian court could not detract from the massive power which the king should be able to mobilize. Alexander's fleet totalled a mere 160 ships, a negligible number for a Greek expedition when Athens alone controlled 400; from Cyprus and Phoenicia, the Persian king could man more than 300 warships with trained native crews and techniques more powerful than any known in Greece. Alexander's money expenses already equalled his father's money income, and a separate debt of 800 talents had accrued for the invasion; the Persian kings received more than 10,000 talents of precious metal as yearly tribute, probably after deduction of the provinces' expenses, and their palaces housed reserves of metal worth 235,000 talents, some in coin, most in the bar ingots which probably served as currency east of Babylon and north to the river Oxus. Alexander's army numbered some 50,000 troops about 6,000 of whom were cavalry; Asia's population numbered millions and only terrain and the problem of supplies limited the Great King's armies. Some 120,000 men or more could be deployed for a decisive battle, 30,000 of whom could be cavalry from tribal nomads and the king's feudal colonists; as for horses, there were ponies to pull chariots, famous studs in north-west Asia and Media, tribes of horsemen in Armenia, Cappadocia and outer Iran, while the lucerne pastures of the Nisaean fields near Hamadan alone pastured 200,000 of the heavy war-horses. In his youth every Persian nobleman had learnt to ride, tell the truth, and shoot a bow; Alexander had a mere thousand archers and slingers and a thousand javelin throwers, whereas the home province of Persia could provide 30,000 trained slingers and archers whose composite bow could kill at a range of 200 yards.