In the centre alone the situation was unmistakable. Alexander's headlong charge towards Darius had carried the right-hand units of Foot-Companions with him, but the left three files, struggling to keep up, had let their line go out of step and exposed a wide gap, as at Issus, in their centre, into which Persians and Indians had poured delightedly, following the daylight through the wall of sarissas. Had they turned against the Foot Companions' ill-armed flanks they could have done untold damage, but they too had scented the distant baggage camp, and so they careered into its midst, slaughtering its unarmed attendants in the hope, perhaps as ordered, of recovering the Great King's family. They had not reckoned with Alexander's line of reserves, whose role throughout is hard to understand. Whether or not they had split, like the front, and allowed the Indians through in the first place, they now patched themselves together enough to face about and fall on the plunderers from the rear. Thanks to Alexander's original precautions, the baggage was finally saved from its various attackers, and Darius's family remained under arrest.

As Alexander routed the Persian centre, he cannot have known that the rest of his line was either endangered or able, most fortunately, to rally its several weaknesses. He may have suspected something of the sort, but he could not possibly have seen it. Dust was swirling around him and it was a matter of dodging the scimitars and lunging at half-seen turbans in order to stay alive: his angled charge had cut in behind the elephants, and the braver foot soldiers had now set about them too, allegedly with bronze tridents designed for stabbing. Their skirmish can only have added to the confusion. The one certain target was Darius, and he was known to have retreated, so Alexander abandoned all secondary dangers and dashed with a group of horsemen in pursuit. If this seems as impetuous as the disastrous conduct of Prince Rupert at Edgehill, it is not to be disbelieved as too irresponsible: through dust and struggling Orientals, Alexander could not usefully have returned in time to aid his left or centre, even had he known this to be necessary. If history later had an excuse to be made, it was not that he set off in pursuit but that this pursuit of a vital prize was to prove a failure. A scapegoat was needed, and as so often, the blame was put down to Parmenion: as Alexander set off on his chase, accompanied by 2,000 cavalry, a messenger, it was said, arrived from Parmenion, begging him to help the left.

This messenger was beset with problems. Different histories time him differently, varying his message and Alexander's retort: some said he voiced a fear for the baggage, whereupon Alexander told Parmenion to forget the bags and fight the enemy, others said he asked for reinforcements, so that Alexander gnashed his teeth and felt obliged to return. It is extremely unlikely that any message ever reached Alexander through the press of a full-blooded battle; it was generally agreed among historians, presumably because Callisthenes first said so, that Parmenion had been slow and incompetent in the fight, and the talc of his 'messenger' could thus be put about by flatterers, in order to explain why Alexander had delayed and failed to catch Darius. His second-in-command, it was pleaded, had held him back, and by the time the excuse was published Parmenion had been killed on a fear of treachery. History, once more, could be rewritten to please Alexander and slander the general he had put to death.

If the pursuit failed, it was more because of the dust and the retreating masses of Persian cavalry; these were trying to break away and follow Darius at the same time as Alexander was trying to cut a path through their lines, and with pursuit and escape at issue the fighting between the two sides was particularly savage. Sixty Companions around Alexander were wounded, Hephaistion among them, before the Persians were finally cleared away; by then Darius was far distant, having crossed the Lesser Zab river. There he had exchanged his chariot for a horse, and ridden away to the Royal Road near Arbela, thirty miles from the battlefield and site of a choice of routes to the heart of his empire. Alexander followed belatedly. By the time he had reached the Zab's far bank the October darkness was beginning to fall and a swift arrest no longer seemed possible. The hones therefore, were allowed to rest, as the pace of the pursuit was already too much for them; not until midnight did they continue south-east to Arbela, where they arrived by Royal Road on the following morning. Inquiries revealed that Darius had long since passed through; he had also left the highway which could have brought him south-east to Babylon, and taken a shorter and less familiar hill route to Hamadan, meeting-point of the roads to his upper satrapies. His trail led through the little-known Kurdish mountains, over passes as high as 9,000 feet, and rather than risk being lost among their hostile nomads, Alexander contented himself with Arbela's handsome store of treasure and the prospect of a safe march south to the riches of Babylon. Darius's escape was a grave disappointment, but men nonetheless were calling him the new king of Asia.

Back on the battlefield, the enemy had soon lost their impulse after the flight of their royal commander. On the right, Bactrians and Scyths had ridden away, unnerved by the mounted sarissa-bearers: in the centre, the Foot Companions had repaired themselves, and on the left Parmenion had somehow repulsed an opposing mass of cavalry, despite their overwhelming numbers and positioning. One dissenting voice maintained that he and his Thessalian horsemen had indeed fought brilliantly, whereas others accused him of sloth and incompetence; the brilliance may be true, and news of Darius's retreat may also have helped him, as may the presence of Mazaeus, who could well have remembered his contacts with Hephaistion a mere month before at the Euphrates. Commander of the entire Persian right, he was not slow to ignore Darius and ride away to Babylon, where he surrendered within weeks and gained his reinstatement. He knew, most suspiciously, where his advantage lay.

In the rout, 'nearly 300,000 Persian dead were counted and many more were taken prisoner, including any elephants and chariots left intact; of those around Alexander, about a hundred were killed, but more than a thousand horses died of wounds or exhaustion during his pursuit'. These absurd figures are history's final comment on a battle which is confused where it is not downright flattery. Alexander's sudden charge from right to centre was evidently crucial, and in the best tradition of attacking generalship; at other points in his line the Persians' obsession with the contents of his baggage camp and their curious inability to turn their numbers to the proper advantage were blessings for which he could claim less credit. It is the mark of a great general to make his enemy seem insubstantial, and Alexander's planning, audacity and speed of decision, had far excelled the enemy command's: he had won magnificently, and he would never have to fight for Asia on any such scale again.

As he returned from his failed pursuit his own position did not yet seem so decisive. At Gaugamela Alexander had seized what a Persian would call his western empire: he had still to approach what Iranians called their homelands. East and south-east stretched the provinces of Medcs and Persians, Bactrians, Sogdians and mountain tribes, to whom Darius could retire from Hamadan and raise a second line of resistance; until Darius was captured, Alexander was not the king of Asia, and he knew it. In the first flush of victory it was still as the Greek avenger that he wished himself to be seen: he wrote to his Greek allies 'that all tyrannies had been abolished and that men were now governed by their own laws', a claim more true of Asia Minor than of mainland Greece, where juntas still flourished under his alliance. His message extended to details too: to the other end of the Mediterranean, he sent spoils of victory to a south Italian town, home, as those Companions who knew the West could remind him, of a Greek athlete who had come to fight a hundred and fifty years before for Greece against the sacrilegious Persian Xerxes.