If he was ruler of Thessaly, he was also by hereditary right the leader of the Greek allies, for Philip had exacted an oath from the Greeks that his newly created office of Leader should pass to his descendants. But his death had started disturbances in every allied city with a grievance, and only by a frighteningly fast march could Alexander win his rightful acknowledgement. Storming through Thermopylae, the narrow Gates of Greece, he carried the central Greek tribes, summoned the Delphic council, a body of more prestige than power, and made them ratify his Leadership, because he controlled them; there had been dissidence in Thebes and Athens, where news of Philip's murder had arrived very quickly from northern agents and caused the people to vote Pausanias the honour of a shrine, but Alexander careered southwards to their borders, scaring Thebes into surrender, Athens into herding her livestock and farmers inside her walls for fear of invasion. Fulsome honours were voted to him, including Athenian citizenship; he accepted them, and passed south to Corinth on the isthmus to summon the allied Greek council of which he was now leader both by example and by right. Not for the last time, he had shown his troops the value of speed, and yet this was the man whom Athenian politicians had predicted would never leave Pella.

War was the natural state of every Greek city. In theory, they were considered to be at war with each other, except for particular cases where they had sworn a temporary alliance and theory was usually born out in practice. The Greece which Philip had outmanoeuvred and Alexander had overawed was a society obsessed with instability and poisoned with revolution. It was not a decadent society, which had somehow betrayed the ideals of a so-called golden age under Pericles's Athens a hundred years before; it was a more level world, both in the balance of power between its states and in the openness of office to men outside its traditional ruling classes. Being more level, it was also more varied. But it was also living proof that for all their variety, the Greeks had failed to produce any political or economic form which could hold a community together or offer to the majority of their citizens a life which was any comfort in a desperately poor landscape with a negligible stock of technology to surmount it. For the past twenty-five years the balance of power in Greece had declined, through feuds between states and upheavals between classes, into an uneasy balance of weakness. Philip had exploited this as an unattached outsider, and his final result, of a common peace among 'free and independent' Greek allies, was intended to stop dissension both between and inside the Greek cities by means to his own advantage. He had already set up friendly governments where necessary, and in the name of stability, Alexander froze them into power by an absolute ban on revolutionary disturbance; in the name of independence, like the Spartans fifty years before him, he broke up the local empires of the larger states on which so much of their mutual aggression had been based, and this measure won him popularity among their many smaller neighbours. Elaborate provisions were made for disputes between cities to be arbitrated, but the detailed clauses of this common peace among allies cannot now be recovered; even if they could they would be as dull as any other dead constitution from the past. The only point which mattered was that Philip and his Macedonians kept control despite their slogan of Greek freedom and that they did not mean to squeeze Greece for tribute or for any cooperation beyond a sullen acquiescence in their aims in Asia.

'Covenants without the sword are but words, and of no strength to secure a man at all'; so Thomas Hobbes wrote in seventeenth-century England, and like Plato and Aristotle, he was mapping out his political philosophy in a real world of revolution and little stability. All three saw the need for authority around them, and Philip and Alexander, no less than Cromwell, appreciated the truth which was written large in the political philosophies of their time. In four key states Macedonian garrisons held the Greeks to their covenants, and if one was removed by Alexander to appease natives who had already rebelled to throw it out, a second was maintained at Thebes, despite similar protest by the Theban people. Events were soon to prove him right; meanwhile, a meeting of his father's allied council confirmed him as supreme general of the Asian expedition, and the last link in the chains of Philip's Greek inheritance had safely been forged for him: 'By his authority he hath the use of so much power and strength conferred on him that by terror thereof, he is enabled to form the wills of them all to peace at home and to mutual aid against their enemies abroad.' More than any clause of Philip's Greek alliance, it is Hobbes's ideal sovereign who sums up the Macedonian leadership of the Greeks.

Only one Greek state stood out against his authority: the Spartans sent Alexander a message saying that it was not their fathers' practice to follow others but to lead them. This splendidly stubborn comment was not as unwelcome as they might have hoped. By their past history in southern Greece, the Spartans had earned the anxious detestation of their smaller neighbours who remembered how Spartan calls to freedom or independence had persistently led to their subjection. Spartan power had been broken for thirty-five years, but it was showing unwelcome signs of a revival, and Philip had played astutely on small neighbours' fears of another Spartan tyranny. Although there were those in more powerful states who called Philip and Alexander the tyrants of Greece, their small and vulnerable neighbours did not see the rise of Macedonia as the death of Greek freedom. Such a concept begged too many questions. Several enemies of Sparta in southern Greece had shown unease at the death of their protector Philip, but Sparta's continued opposition to Alexander reminded them that their best hope of protection lay with a Macedonian leader.

So it suited Alexander to leave Sparta alone, and instead he had words with a Greek philosopher whom he happened to find in Corinth's suburbs. Diogenes, founder of the Cynic school, was visiting Corinth and as a believer in the vanity of wordly riches, he was living in a wooden tub: passing by, Alexander saw him and asked if there was anything this abject figure wanted. Yes, replied Diogenes, stand aside a little, for you are blocking the sun. One of his pupils later joined Alexander as an admiral and wrote a colourful history, including the story of this meeting, but it was probably his fiction that Alexander went on to comment: 'If I had not been Alexander, I would like to have been Diogenes.' And yet both of them shared, for different ends, an extraordinary power of physical endurance.

As winter began, Alexander left Corinth and returned northwards, stopping to make a dedication at the Delphic oracle. His visit was the start of a new and persistent theme. The priesthood had always repaid Philip's favours, but Alexander, it was said, was refused an oracle because he had come on an unfavourable day. He man-handled the priestess and dragged her to the shrine, and during the struggle she acknowledged him as invincible. These 'unfavourable days' are not known until Roman times and the story of the struggle and refusal is likely to be a Roman slander, belittling Alexander's invincibility against that of their own emperors. But the theme is rich in consequences. The troops would believe that the Delphic oracle had somehow guaranteed it, probably because Alexander encouraged the story at Delphi himself. When he was later proposed for divine honours at Athens as an invincible god, the title must have been known to be his favourite. No man, and only one hero, had been called invincible before him, and then only by a poet, but the hero was Heracles, ancestor of the Macedonian kings. Alexander emphasized the theme of Victory on his coins, in his dedications and the names of his cities, and as a result of his exploits, a newer and mightier Heracles the Invincible entered into Greek and Roman religion. In Iran, his Successors continued the titles he had begun, and the idea of Invincibility passed from the Greek East to Caesar and finally to the Sun whose worship grew to rival Christ's. When Alexander began to stress this powerful link with Victory and the hero Heracles, whose assistance he constantly recognized, a new concept was born for divine kingship. It was the first, and not the least, of his legacies to religion and it also caught his confident mood; on returning to Macedonia, he called out his father's army for training and drill, and on this army, more than any claim to victory, his invincibility always depended. To modern field-marshals the Macedonian army has seemed the most enviable force in history. Its design is intriguing and leads straight to Philip, the most immediate reason why Alexander ever became great.