He was encouraged in his choice by a local windfall. Meshed lay on the border of the ancient satrapy of Aria, which the Persians called Hariva, and as its name implied, it was a heartland of Iranian tribesmen who had lived there for at least five hundred years; the title Ariana, whence modem Iran, was already applied to the eastern lands beyond it, even as far as the Punjab borders. Possibly it was from Aria, centred on the oasis Hariva and watered by the Hari-Rud river that the Iranians had first swept westwards in their early tribal wanderings: such a history would have made it an awkward province for Darius's heir to pass through, let alone to control, had not its satrap Satibarzanes come to Meshed and surrendered on the border. Leader of the Arians' cavalry at Gaugamela and then, like Bessus, a murderer of Darius, he was nonetheless restored to his high office and given an advance squadron of mounted javelin-throwers, Iranians like himself, to police the Macedonians as they passed along the edge of his province, only too keen to plunder it for supplies. Favouring one royal assassin, therefore, Alexander prepared to pursue another, but first all excess baggage was piled on to wagons and massed in the centre of the camp; Alexander then set fire to it, his own wagon first, the others only when his own example had been observed. From now on, pack-animals would serve as transport on roads too rough for wheels. The army acquiesced in the sudden loss of their luggage, knowing that Alexander had suffered too; at least they were allowed to keep their native concubines.

Satibarzanes left with his guards for the distant capital of his province and from Meshed in mid-August, Alexander continued east towards the Silk Road, still meaning to dislodge the pretender Bessus from his distant base at Balkh. He had not gone far along the edge of the Arians' satrapy when grave news compelled him to hurry south to its heart; Satibarzanes had murdered his guards, raised 2,000 horsemen in revolt and blockaded his capital's fortress. In two days Alexander raced a picked force southeast down the seventy miles to Artacoana, the capital city, where reprisals could only be merciless as trust had been badly betrayed. The rebels took refuge on a steeply wooded hill, but the undergrowth was fired until those who stood their ground were smoked and burned to death; at Artacoana, siege towers breached the city walls and all troublemakers were set aside for death or enslavement. Alexander ordered the rest to be resettled on the site which was to be renamed Alexandria and strengthened by new walls and Macedonian veterans. The result still survives in Herat, its modem successor, but not for the last time in the East, an Alexandria had merely developed the buildings of an ancient Persian citadel and satrapal court. Satibarzanes, meanwhile, was nowhere to be found. On news of Alexander's advance he had escaped up the Hari Rud valley and disappeared into the foothills of the Hindu Kush to collaborate with Bessus. He had been a bad mistake, and he was to prove persistent.

Rather than pursue him Alexander reversed his plans. He would no longer return to the north-eastern Silk Road and approach Bessus's henchmen directly; he would entrust Aria to a Persian, perhaps the son of Artabazus, his most trusted Oriental, and follow the more devious route due south, to Seistan, the Helmand valley and eventually the passes over the central Hindu Kush. It was a momentous decision, rich in surprises and hardships but not without strategic sense. Satibarzanes was still un-captured on the shorter alternative road and Alexander would not have wished to encounter him and Bessus for the first time in late autumn, in an arid valley which allowed an ambush. Seistan's satrap, too, was known to have murdered Darius. If ignored he might rally to Bessus and block Alexander's rear. Of the three enemies he should be routed first.

Emboldened by 6,000 reinforcements who had arrived from Antipater and the West, Alexander marched as he pleased from Herat to the borders of Seistan, so scaring its satrap, also a murderer of Darius, that the man fled away to the nearest Indians of the Punjab. But they soon arrested him and sent him back to be executed 'for his crime against Darius'; Alexander, by then, had learnt the perils of mercy and preferred to appear as Darius's righteous avenger. In early autumn, Seistan is not a place in which to give enemies a second chance: its dusty plains are scoured by the seasonal Wind of a Hundred and Twenty Days, which pipes down through the cliffs and sand-dunes of the north-west and rolls the earth into such clouds of greyness that a man has to struggle to stand, let alone to march with a sarissa. Tufts and bushes of greenery are stripped of their leaves, a discomfort for Alexander's horses which had already browsed imprudently among the poisonous spurges near Herat. As for the 32,000 troops, they were short of food in a land where the harvest is garnered early in order to escape the cutting winds: tents, therefore, were tugged down for nine days' rest at Farah, site of the local satrap's palace on the northern edge of modern Seistan.

Hungry and buffeted by the wind, the troops might be forgiven for envying Parmenion his opportune absence in Hamadan. For the past three months the elderly general had remained on communications, perhaps a sign of impending retirement, for he was already in his seventieth year. His absence tended to support this suspicion. His last known orders had been to join Alexander in Gurgan in July but he had never arrived and it was charitable to guess that the orders had been cancelled in favour of staying his ground. He had been left with some 25,000 men, the Thracians, the veteran mercenaries, the Thessalians, the Paconian horsemen and 6,000 Foot Companions whose four battalions had been ordered to supervise the arrival of the treasure in Hamadan. Cleitus had been instructed to take these four battalions ahead as soon as their job was finished, but they had not reached Alexander by the time he arrived in Seistan. Even if they were already on the road from Hamadan, Parmenion retained a sizeable force. He still controlled nearly twenty thousand troops at a time when Alexander had little more than thirty thousand in his own camp. The balance of forces happened to be nearly equal between king and general; at Farah the general was to spring for the last time into memorable prominence: 'Safe from outside, Alexander was suddenly attacked from within his household.' It was a most mysterious affair. Those who might have known the truth said little about it: others elaborated, guessing freely on the basis of rumour and hearsay.

According to Ptolemy, a plot was revealed to Philotas, Parmenion's son, who failed to pass the report to Alexander even though he visited the king's tent twice every day. A second version fills in the details, and in the absence of anything more convincing it has to be believed. The affair was said to have begun when a Macedonian called Dimnus told his boy-lover that a plot was afoot to kill the king. He gave the names of the conspirators and he revealed in extreme secrecy that their attempt was to be made in three days' time. But his lover was young and indiscreet. He told the secret to his brother Cebalinus and like all young men who give away secrets, asked him to do what he had not: keep the plot to himself. But Cebalinus lost his nerve. He was shocked and he did not wish to be an accessary to murder, so he went to the highest officer he knew and told him all his brother had let slip. The officer was Philotas, son of Parmenion.

Twice daily, Philotas would go to Alexander's tent but for two days he put off Cebalinus's inquiries, saying that the king had been busy and there had been no chance to raise the matter in his presence. Cebalinus became suspicious. Time was running short, so he turned to one of the royal pages whom he found on guard in the armoury. The page had intimate access to the king and at once he made for the royal bathroom where he found Alexander having his bath. The plot was reported and those concerned were ordered to be arrested. Cebalinus told his story, excusing himself as a loyal informer; Dimnus was summoned as the source of the evidence, but killed himself, probably before he could be questioned. The king had lost his prime witness and was left with a garbled list of names, passed by Dimnus to his boyfriend and by the boyfriend to his brother. Only one clear fact had emerged: Philotas had been told of a plot, but had suppressed the news for the past two days. That needed rapid investigation.