The next task was to secure the lower slopes of the mountain from the few remaining guards. A troop of Companions galloped up to dismount and do battle, but the guards fled again at their onset and the hill passed to Alexander and his skirmishing force of Agrianians, archers and Shield Bearers. While they held the slopes against the enemy higher up the mountain, the rest of the army forded the river on one side of the narrows, continuing the war-cry and forming swiftly up on the far bank to deter attackers; Alexander held their rear with his trusted skirmishers and only joined them when it seemed safe. More shouting and firm drill from, the infantry scared off the worst of the danger, and when Alexander was finally forced to ford the river himself, he arranged for arrow-shooting catapults on the far bank to give him cover across the water. Holding off with his skirmishers, covering with his artillery, and menacing with his heavier troops, he escaped disaster by an intelligently balanced withdrawal. Three days later he slipped back by night across the river and launched two brigades of Foot Companions and his invaluable archers and Agrianians into an enemy who were casually encamped and not expecting to see him again. Many were slaughtered, more captured and the Illyrian kings fled northwards, discredited.

But unwelcome news prevented any further pursuit. It was already mid-September and by circling round his northern frontiers, Alexander had presumed on the obedience of the Greeks and the continuing safety of Philip's advance force in Asia. On both points he was mistaken. In Asia, Attalus had been murdered, and it was perhaps on news of this that Olympias had taken vengeance into her own hands in Macedonia and murdered Eurydice, niece of Attalus and the girl who had supplanted her in Philip's affections; for completeness, she had murdered her baby daughter Europe too. But in Asia, perhaps because of Attalus's removal, the advance force had faltered and been driven back by the vigour of the Persian king's generals; as part of a coherent strategy, 300 talents were said to have been sent to Demosthenes, most hostile of Athenian politicians, and there were hopes that the Greeks would rebel against their leaders. Rebellion had indeed come, but it owed nothing to Persia or to Athenian politicians.

Three years before Philip had punished the city of Thebes in central Greece harshly for her opposition on the battlefield; she had been his ally, then changed sides as her hopes were disappointed; after the Greeks' defeat, she had seen her prisoners sold as slaves and her dead buried only after she had paid for the privilege. In the city prominent Thebans were killed or exiled and their property was confiscated; a Macedonian garrison invested Thebes's fortress and a council of three hundred Thebans, many of whom had already been exiled by their fellow citizens, were set in authority over men who loathed them for their debt to Macedonia. Worst of all, in the name of independence Philip had promised to restore the smaller cities in surrounding Boeotia; these cities Thebes had persistently tried to tyrannize for the sake of more land and power, and nearly two hundred years of Theban history could be written round her domination of small and reluctant neighbours. Now they were to be independent, by order of a Macedonian.

It was not, then, Alexander who was to blame for Thebes's latest upheaval. Philip's severity was working itself out in Alexander's name, and the cause was the secret return of Thebans whom Philip had banished three years before. They talked of freedom and they alleged that Alexander had been killed in battle near the Danube. This sounded too convincing to resist, and when they described the misbehaviour of the Macedonian garrison, whom the Thebans had been too slow to eject the previous autumn, two of its leaders were seized and assassinated. It was open rebellion, now, but their talk of freedom was hardly disinterested: among the returned exiles, there were former officials of the league through which Thebes had dominated her neighbours, and if they were protesting against Macedonia's tyranny, they were also indignant that their own sweet days of local empire had ended.

Alexander treated the news with the speed and gravity which it deserved. He did not waste time in returning to Macedonia, but in a tremendous forced march he stormed down Macedonia's western border, across the brown plains near Trikkala, and was over all hills and mountain passes and up before Thebes within fourteen days. Thebes had been hoping for Athenian troops and for citizen armies from southern Greek cities, but only the Arcadians were stirring to join her, and other states seemed dangerously likely to stay neutral or even to help the Macedonian leader to whom they were sworn allies. When a Macedonian army, more than 30,000 strong, was reported from the city walls, the Thebans could not bring themselves to believe it: 'Alexander', they assumed, must be Antipater, or perhaps Alexander of Lyncestis who had been set in command of Thrace. But to their cost, Alexander it was, and within a week he had begun the 'swiftest and greatest disaster', it could be said, which had ever befallen a Greek city.

Alexander's movements were decisive and much deplored, and the dispute, as often, left its mark in the delicacies of his various histories. Ptolemy, his friend and officer, stressed his reluctance to attack the city, his repeated delay in the hope that Thebes would send ambassadors, the division, no doubt true, between Thebans who wished to talk and between instigators who would have none of it; others agreed on the fact of Alexander's delay, but when Alexander asked for the surrender of the rebel leaders, the Thebans, they said, answered him by shouting from a high tower for help in freeing the Greeks from their tyrant, and Alexander thereupon launched irrevocably into plans for attack. Three days later he opened battle with the Theban army outside the walls and was very hard pressed indeed, for the Thebans had been training in their city gymnasium; not until Antipater led his reserve line into action did his Macedonians begin to recover ground. As they rallied Alexander noticed a postern-gate in the city wall which the Thebans had left unguarded, and this turned the battle. He hurried Perdiccas and his regiment to take it, and once the city had been entered behind the Thebans' backs, their defence was vain; the looting was helped by the Macedonian garrison who had hitherto been blockaded inside their fortress, and it knew no bounds.

Ptolemy put it more cunningly: so far from attacking intentionally, Alexander had continued to delay, and it was only when Perdiccas acted without orders and took it into his head to attack the Thebans' stockade that battle was joined at all. For Perdiccas tried an unofficial raid and was 'wounded badly', and 'almost stranded'; only when the Thebans drove his men back into Alexander's camp did Alexander feel obliged to charge to the rescue. As if by accident, some of the Macedonians followed up so fast that they were trapped inside the city itself; they were almost unopposed, and with the garrison's help, the city fell to them, more by accident than savage design. This sly apology is very interesting. Writing after Alexander's death Ptolemy had strong reason to slander his rival and enemy Perdiccas, and so he explained away Thebes's capture as due to his insubordination and the chance reprisals of his master Alexander. He also posed as a protector of Greek freedom and had reason to conceal Greek opposition to the Macedonians.

And yet one fact was agreed, and of great significance. In the brutal sack of the city, Alexander's Greek allies from Thebes's neighbouring cities distinguished themselves by looting worthy of any Thracian, and given their past history, their enthusiasm was wholly forgivable. In Greece Philip had repeatedly supported the smaller cities against their bigger neighbours; now, when Alexander dismantled the power of Thebes, it was these small cities who joined him wholeheartedly as allies. The sack of Thebes cannot be dismissed as one more outrage to the freedom of the Greeks, for Thebes herself had infringed that freedom by her local empire, and fellow Greeks had avidly repaid in Alexander's name all that they had suffered from Thebes in the past. Alexander shrewdly entrusted the fate of the city to the decision of these allied Greek assistants, probably at a meeting on the spot rather than at a full council of his 'allies' in all Greece. They voted for Thebes's utter destruction, as he knew they would. So the city was destroyed, all private ground was given to the allies to farm as a reward, and 30,000 Thebans are said to have been enslaved, women and children included; they were sold at a reasonable price for such a sudden glut on the local market. Priests were exempted, as were the known opponents of the rebellion and all friends and representatives of the Macedonians' interests, down to the descendants of the poet Pindar, who had written poems to the Macedonian king a hundred and fifty years before. His house, conspicuously, was bidden to be spared.