With Bessus safely in chains, the march northwards might have ended, had it not been natural to ride on to the nearby river Jaxartes and claim the north-east frontier of the Persian empire. Near Karshi, Alexander recruited the fine-blooded local horses to replace the many who had died in the desert; near Kungurtao, the one hill in the sandy monotony of the landscape, his men were harassed by natives while looking, perhaps too desperately, for food. Reprisals are said to have killed some 20,000 natives, though they did manage to hit Alexander hard in the leg with an arrow and break his splint-bone, a danger in a desert climate which invited gangrene. The wound caused a quarrel, not a delay, for Alexander was determined 300 to be carried on a stretcher to keep the expedition moving, and the choice of suitable bearers divided the army. Cavalry and infantry quarrelled for the privilege, a rift which would reopen six years later after Alexander's death. But in Sogdia Alexander was there to settle it and arrange that cavalry and infantry should take the job in turn. Loyalties were satisfied and within four days of desert marching, the army reached Samarkand, as yet a mere mud-walled summer palace of the ruling Iranians, watered by a river which the troops named Polytimetus, the Greek for 'very precious', no doubt a reference to the gold which was washed down its bed and is still remembered in its modern name Zarafshan or 'Scatterer of gold'. From here it was only 180 miles to the frontier river. Native villages were looted for food, burnt where resistant. Alexander, presumably, was still unable to walk.

The frontier was reached in July when humidity sinks as low as five per cent and the shade temperature rises to 43 ⁰C. At modern Kurkath, a few miles south of its main ford, the river was guarded by a Persian outpost which Cyrus had settled two hundred years before, and as in the Hindu Kush, Alexander ordered a new Alexandria to replace it: 'He thought that the city would be well sited and suitable for increase, especially as a guard against the tribesmen beyond, and he expected that it would become great both from the numbers of settlers merged into it and from the splendour of its name.' On the last point, he was mistaken; Alexandria-the-furthest was soon harassed by nomads and refounded by his successor as an Antioch, it then became known as modem Khojend, then, as other names seemed splendid, Stalinabad, then Leninabad.

The city's purpose was unmistakable: improved defence of a frontier which had loomed large in the Persians' past. By viewing Persia through the eyes of a western Greek, this anxiety has often been underestimated. To Persians of the future, it was not the defeats by the Greeks at Marathon which lived on as an uneasy memory so much as the fact that their great king Cyrus and their prophet Zoroaster had both died fighting against nomads of the northern steppes. The province of Sogdia was to Asia what Macedonia was to Greece: a buffer between a brittle civilization and the restless barbarians beyond, whether the Scyths of Alexander's day and later or the White Huns, Turks and Mongols who eventually poured south to wreck the thin veneer of Iranian society. In this barrier province, Alexander naturally followed his father's example and strengthened Sogdia, like Philip's Macedonia, with improved towns and military colonies to keep the Scyths where they belonged. Already envoys had crossed the Jaxartes river to talk to the Scythian king and spy out his peoples, the most expert horsemen known to cast Iran. They were mobile and dangerous and the glorious art of their bridles, cups, carpets and tents is a reminder that the palace world of Asia and the city life of its Greeks were only brief punctuations in an older world of nomads, as light as dust but no less permanent, and never a society to be undervalued. It was an omen of the times that in a Persian love story, translated into Greek by Alexander's court usher, the villain of the piece had been changed since the mid-sixth century from a Bactrian aristocrat to a Scythian chieftain.

Before Alexandria-the-furthest could be begun, news arrived of rebellion, not among the Scyths, but in the rear. Since landing in Asia, Alexander had asked his men to march dreadfully hard, often without food, but he had never entangled them in a slow and self-sustaining struggle with guerrillas. Now for the first time his speed was to be halted. This Sogdian rebellion would exhaust his army's patience for eighteen unsatisfactory months, make new demands on his generalship and induce a mood of doubt among his entourage. The causes were simple; four of Bessus's henchmen still ranged free, led by Spitamenes the Persian whose name has a link with the Zoroastrian religion. All four now began to work on the native mistrust of the Macedonians. There was ample reason for it. Anxiously searching for food in the Sogdian desert, Alexander's army had plundered ricefields, looted flocks and requisitioned horses, punishing all resistance severely. His thirty thousand soldiers could not be fed from any other source, but it was a dangerous way to behave. Meanwhile, the natives saw garrisons installed in their main villages; Cyrus's old town was being changed into an Alexandria, and already, as in Bactria, Alexander had banned the exposure of dead corpses to vultures, because it repelled his Greek sensitivities. Like the British prohibition of suttee in India, his moral scruples cost him popularity, for Sogdians had not seen Persia overthrown only to suffer worse interference from her conquerors. It was time to be free of any empire, especially when a conference had been ordered at Balkh which the local baronry were expected to attend. If they went they might be held hostage. Bactrians, therefore, joined the resistance, the same Bactrians no doubt, whom Bessus had timorously abandoned, and from Balkh to the Jaxartes Alexander found his presence challenged.

Ignoring the nomad skirmishers who had gathered to rouse the south along the Oxus, Alexander turned against the nearest rebellious villagers. Here his garrisons had been murdered, so he repaid the compliment to the seven responsible settlements in a matter of three weeks. The mudbrick fortifications of the qal'ehs were treated contemptuously. Though siege towers had not yet been transported over the Hindu Kush, collapsible stone-throwers were ready to be assembled if necessary; they were not needed at the first three villages, which succumbed in two days to the old-fashioned tactics of scaling parties backed up by missiles; the next two were abandoned by natives who ran into a waiting cordon of cavalry, and in all five villages the fighting men were slaughtered, the survivors enslaved. The sixth, Cyrus's border garrison at Kurkath, was far the strongest, because of its high mound. Here, the mud walls were a fit target for the stone-throwers, but their performance was unimpressive, perhaps because there was a shortage of ammunition; stone is very scarce in the Turkestan desert and it cannot have been possible to transport many rounds of boulders across the Hindu Kush. However, Alexander noticed that the watercourse which still runs under Kurkath's walls had dried up in the heat and offered a surprise passage to troops on hands and knees. The usual covering fire was ordered and the king is said to have wormed his way with his troops along the river-bed, proof that his broken leg had mended remarkably quickly. The ruse was familiar in Greece, and once inside, the gates were flung open to the besiegers, though the natives continued to resist, and even concussed Alexander by stoning him on the neck. Eight thousand were killed and another 7,000 surrendered: Alexander's respect for his newfound ancestor Cyrus did not extend to rebellious villagers who wounded him, so Kurkath, town of Cyrus, was destroyed. The seventh and final village gave less trouble and its inhabitants were merely deported.