Only in infantry was the Great King at a disadvantage. He had his trained palace foot-guards, 10,000 in all, but the hot climate, the lack of a class of small farmers and the traditions of archery and riding among his colonists meant that the empire had no heavy infantry apart from the Honoured Equals of its court. Greek infantry had served in the armies of Egypt's Pharaohs for the past three hundred years, and the Persian kings had taken to hiring them too; 50,000 Greeks, as many as Alexander's entire army, are said, with only slight exaggeration, to have fought against Alexander's crusade, most of them hired for the occasion, few of them retained as garrisons and none on permanent duty east of the Euphrates. There is no more vivid reminder of the facts of life in ancient Greece. Fifty years of Greek revolutions and domestic wars had swelled the hordes of exiles which Philip's diplomacy had anyway encouraged. Continuous and savage poverty in Greece had always made salaried service in Asia the landless man's most plausible means of survival and social betterment, a means far more certain than the hazardous gambles of sea trade or the temporary life of hired labouring in a world well stocked with slaves. The imaginative became pirates, the rest were mercenaries; sons with no inheritance, bored or incompetent farmers, failed merchants, bastards, all could look for a new start, their keep, and an adventure if they took to fighting in Asia. Some were desperate through famine, others through exile; some had fled to fight the Macedonians whom they hated, others simply liked soldiering, or had stayed on as veterans of recent campaigns in Egypt and the Levant. Most had been unable to settle, some did not wish to; their ruthless roaming had long been the horror of landed Greek gentlemen, and among conservative Greek opinion there would be no regrets that Alexander the Greek Leader was invading the barbarians to do battle, on foot, with Greeks who threatened the security of every gentleman's estate.

To every Persian statistic, there were to be reservations, but there was one figure which could not be gainsaid; the Persians ruled an empire of vast horizons, too vast for the Greeks to know their extent. To Aristotle the world's edge came beyond the Hindu Kush mountains in Afghanistan, and although he knew that the Caspian Sea was not an ocean, the depth of Asia from the Black Sea to the Persian Gulf was narrowed in his mind beyond all recognition. Yet under one and the same allegiance, tall Persian towers surveyed the fox-fur traders of the upper Oxus and the spice-bearing caravans from the Arab sheikhs of the Hadramut; the teak woods of the Punjab, the tiger forests of Gurgan, the cedar woods of Lebanon and the pitch-pine slopes of Mount Ida acknowledged the King of Kings' wishes at a range of 5,000 miles; salts were sent to his table by the priesthood of the Libyan desert; lapis lazuli adorned his palace from the blue mines of Badakshan; for two hundred years, the Persian Empire had kept an open road for the cultures of the East, bringing iron through invasion to the Negroes of the Sudan, Greek bridge-builders from the Aegean to the Euphrates, peaches, peacocks and the water-goddess of Iranian nomads to the temples and villages of Greek Asia Minor. All the while, the Persian kings had shifted their court from winter to summer palace at their empire's centre, as much as three months' journey from the Aegean coast and yet still in close touch with emergencies through their Royal Road and their enviably swift system of fire signals, by whose beacons and bonfires news could travel from Sardis to Susa in less than a week. Beyond them, mountain pressed on broad grass prairie, desert was broken by mirror-like fields of green rice; language was as varied as the Empire's many landscapes, and for uniformity, among themselves, the Persians' governors ruled in an official tongue which they could not speak or write grammatically. Without maps and ready interpreters, it was through this variety that Alexander was meaning to find both a living and a way.

It is, therefore, the scale of his organization which impresses and puzzles most. He is known to have taken Greek surveyors, men trained as long distance runners who paced out the roads of Asia and recorded their distances; one of them, a Cretan, had already distinguished himself with a famous run across southern Greece, bearing news from city to city of Alexander's sacking of Thebes. Greek doctors of the Hippocratic school gave their services for the sick and wounded, and Greek prospectors were to search out minerals, whether the rubies of India or the red gold of Kirman, for Alexander had his father's keen eye for mineral resources. Of the cooks, the grooms and the leather workers history has left no word; Greek and Phoenician engineers are known, but the soldier carpenters who planed the planks for the ship timbers and maintained the army's wagons are never mentioned, though they must have numbered thousands. As servants were limited, the unsung heroes of the expedition are to be found, as always, among the supplies. Even if money was paid for each individual to buy what he could, then cook it himself, there were formidable tasks of organization. Bread, fruit and cheese were the staple diet of the soldiery, and although hand-mills were taken with the army for grinding grain on the march, the grain itself had to be bought in a market arranged with free enterprise, the satraps or the local towns. Invaders can hardly delay to reap their enemy's com for themselves, but in their first four years, the army is never known to have starved. Transport was essential for such efficiency and, except by water, it was slow and costly; the fleet could ship the army's food along coasts and rivers, but inland, a week's supplies for 50,000 troops could rarely be transported, and the interminable train of oxdrawn carts or mules and panniers would have been impossible except on the level surface of a road. Of all Alexander's friends in Asia, the Royal Road which ran between post-houses from Sardis to Susa was far the most precious; by this one road which they inherited and improved, the Persians had bared their empire to invasion, for Alexander had no more accurate directions through Asia than Herodotus's history, Xenophon's memoirs of his march and the stray advice of local friends and guides. But he had only to follow the Royal Road and its daily staging posts and he would one day reach a palace; it is more true to say that Alexander conquered Asia's main roads than that he conquered Asia.

The campaign, which he accepted from his father, was proclaimed as a march against barbarians, and yet of all its untruths, this, as he found, was to prove the worst. It was more than two hundred years since the Persians had turned from nomads into a ruling court and the Great King's audience-tent and his ritual accession still recalled those old nomadic days of the self-sufficient life of moving flocks. But since leaving the proudest way of life in history, they had turned into a society which many have envied as civilization, rich in the rural life of landed gentlemen where men have the time to plant trees and tend their game parks, hunt and keep ornamental birds. In the courts and castles of a satrap, men could lay out an intimate garden and set off their loggias with quincunxes and canals; 'wherever the Persian king stays, his concern is to create stupendous gardens, called paradeisoi, filled with the choicest fruits and flowers of that land ... how fine and even the trees are, how straight their rows, how exactly arranged at right angles, how heady the scent of the flowers!' Greek gardens of vegetables and herbs never rose to such a high art and the flowerpots let into the surrounds of one of Athens's temples were in the worst municipal taste. Similarly, no Greek ever wrote a prose work worth reading as fiction until the influence of Persian romances and love stories had worked into their imaginations. The Persian kings, wrote Aristotle's pupils, had promised rewards to inventors of new pleasures, and so hastened defeat by their sensuality; there were harems, certainly, but there were also purple dyes and beautifully patterned carpets, spices, cosmetics, haute cuisine, fantastic dances, furs of ermine and snow leopard, golden and ivory harness and gem-set rings of carnelian and lapis lazuli; it was remembered how when a satrap had visited Greeks, he had brought Persian servants as the only men who knew how to make up a comfortable bed. The society which Greeks called slavish was also expressive and spiritual; nudity was a disgrace, justice severe and women respected with courtesy, and as an obedient community, content to follow their nobles, it was not surprising that the Iranians should have worshipped and spread the worship of Anahita, the most appealing goddess before the virgin Mary, who moved west from her home as water goddess of the Oxus and grew to dominate the huntress Artemis, goddess of Greeks in Asia. It is more remarkable, though disputed, how the philosophic wisdom of their prophet Zoroaster may have influenced the most admired intellectuals of the Greeks themselves.