Here are his thoughts and reasonings:
Nothing can be thought to be further from my aim since I commenced this task than to digress more than is necessary from the order of the narrative or by embellishing my work with a variety of topics to afford pleasant resting-places, as it were, for my readers and mental relaxation for myself. The mention, however, of so great a king and commander induces me to lay before my readers some reflections which I have often made when I have proposed to myself the question, "What would have been the results for Rome if she had been engaged in war with Alexander? "The things which tell most in war are the numbers and courage of the troops, the ability of the commanders, and Fortune, who has such a potent influence over human affairs, especially those of war. Any one who considers these factors either separately or in combination will easily see that as the Roman empire proved invincible against other kings and nations, so it would have proved invincible against Alexander. Let us, first of all, compare the commanders on each side. I do not dispute that Alexander was an exceptional general, but his reputation is enhanced by the fact that he died while still young and before he had time to experience any change of fortune. Not to mention other kings and illustrious captains, who afford striking examples of the mutability of human affairs, I will only instance Cyrus, whom the Greeks celebrate as one of the greatest of men. What was it that exposed him to reverses and misfortunes but the length of his life, as recently in the case of Pompey the Great? Let me enumerate the Roman generals - not all out of all ages but only those with whom as consuls and Dictators Alexander would have had to fight - M. Valerius Corvus, C. Marcius Rutilus, C. Sulpicius, T. Manlius Torquatus, Q. Publilius Philo, L. Papirius Cursor, Q. Fabius Maximus, the two Decii, L. Volumnius, and Manlius Curius. Following these come those men of colossal mould who would have confronted him if he had first turned his arms against Carthage and then crossed over into Italy later in life. Every one of these men was Alexander's equal in courage and ability, and the art of war, which from the beginning of the City had been an unbroken tradition, had now grown into a science based on definite and permanent rules. It was thus that the kings conducted their wars, and after them the Junii and the Valerii, who expelled the kings, and in later succession the Fabii, the Quinctii, and the Cornelii. It was these rules that Camillus followed, and the men who would have had to fight with Alexander had seen Camillus as an old man when they were little more than boys.
Alexander no doubt did all that a soldier ought to do in battle, and that is not his least title to fame. But if Manlius Torquatus had been opposed to him in the field, would he have been inferior to him in this respect, or Valerius Corvus, both of them distinguished as soldiers before they assumed command? Would the Decii, who, after devoting themselves, rushed upon the enemy, or Papirius Cursor with his vast physical courage and strength? Would the clever generalship of one young man have succeeded in baffling the whole senate, not to mention individuals, that senate of which he, who declared that it was composed of kings, alone formed a true idea? Was there any danger of his showing more skill than any of those whom I have mentioned in choosing the site for his camp, or organising his commissariat, or guarding against surprises, or choosing the right moment for giving battle, or disposing his men in line of battle and posting his reserves to the best advantage? He would have said that it was not with Darius that he had to do, dragging after him a train of women and eunuchs, wrapped up in purple and gold, encumbered with all the trappings of state. He found him an easy prey rather than a formidable enemy and defeated him without loss, without being called to do anything more daring than to show a just contempt for the idle show of power. The aspect of Italy would have struck him as very different from the India which he traversed in drunken revelry with an intoxicated army; he would have seen in the passes of Apulia and the mountains of Lucania the traces of the recent disaster which befell his house when his uncle Alexander, King of Epirus, perished.
[9.18]I am speaking of Alexander as he was before he was submerged in the flood of success, for no man was less capable of bearing prosperity than he was. If we look at him as transformed by his new fortunes and presenting the new character, so to speak, which he had assumed after his victories, it is evident he would have come into Italy more like Darius than Alexander, and would have brought with him an army which had forgotten its native Macedonia and was rapidly becoming Persian in character. It is a disagreeable task in the case of so great a man to have to record his ostentatious love of dress; the prostrations which he demanded from all who approached his presence, and which the Macedonians must have felt to be humiliating, even had they been vanquished, how much more when they were victors; the terribly cruel punishments he inflicted; the murder of his friends at the banquet-table; the vanity which made him invent a divine pedigree for himself. What, pray, would have happened if his love of wine had become stronger and his passionate nature more violent and fiery as he grew older? I am only stating facts about which there is no dispute. Are we to regard none of these things as serious drawbacks to his merits as a commander? Or was there any danger of that happening which the most frivolous of the Greeks, who actually extol the Parthians at the expense of the Romans, are so constantly harping upon, namely, that the Roman people must have bowed before the greatness of Alexander's name - though I do not think they had even heard of him - and that not one out of all the Roman chiefs would have uttered his true sentiments about him, though men dared to attack him in Athens, the very city which had been shattered by Macedonian arms and almost well in sight of the smoking ruins of Thebes, and the speeches of his assailants are still extant to prove this?
However lofty our ideas of this man's greatness, still it is the greatness of one individual, attained in a successful career of little more than ten years. Those who extol it on the ground that though Rome has never lost a war she has lost many battles, whilst Alexander has never fought a battle unsuccessfully, are not aware that they are comparing the actions of one individual, and he a youth, with the achievements of a people who have had 800 years of war. Where more generations are reckoned on one side than years on the other, can we be surprised that in such a long space of time there have been more changes of fortune than in a period of thirteen years ? Why do you not compare the fortunes of one man with another, of one commander with another? How many Roman generals could I name who have never been unfortunate in a single battle! You may run through page after page of the lists of magistrates, both consuls and Dictators, and not find one with whose valour and fortunes the Roman people have ever for a single day had cause to be dissatisfied. And these men are more worthy of admiration than Alexander or any other king. Some retained the Dictatorship for only ten or twenty days; none held a consulship for more than a year; the levying of troops was often obstructed by the tribunes of the plebs; they were late, in consequence, in taking the field, and were often recalled before the time to conduct the elections; frequently, when they were commencing some important operation, their year of office expired; their colleagues frustrated or ruined their plans, some through recklessness, some through jealousy; they often had to succeed to the mistakes or failures of others and take over an army of raw recruits or one in a bad state of discipline. Kings are free from all hindrances; they are lords of time and circumstance, and draw all things into the sweep of their own designs. Thus, the invincible Alexander would have crossed swords with invincible captains, and would have given the same pledges to Fortune which they gave. Nay, he would have run greater risks than they, for the Macedonians had only one Alexander, who was not only liable to all sorts of accidents but deliberately exposed himself to them, whilst there were many Romans equal to Alexander in glory and in the grandeur of their deeds, and yet each of them might fulfil his destiny by his life or by his death without imperilling the existence of the State.
[9.19]It remains for us to compare the one army with the other as regards either the numbers or the quality of the troops or the strength of the allied forces. Now the census for that period gives 250,000 persons. In all the revolts of the Latin league ten legions were raised, consisting almost entirely of city troops. Often during those years four or five armies were engaged simultaneously in Etruria, in Umbria (where they had to meet the Gauls as well), in Samnium, and in Lucania. Then as regards the attitude of the various Italian tribes - the whole of Latium with the Sabines, Volscians, and Aequi, the whole of Campania, parts of Umbria and Etruria, the Picentines, the Marsi, and Paeligni, the Vestinians and Apulians, to which we should add the entire coast of the western sea, with its Greek population, stretching from Thurii to Neapolis and Cumae, and from there as far as Antium and Ostia - all these nationalities he would have found to be either strong allies of Rome or reduced to impotence by Roman arms. He would have crossed the sea with his Macedonian veterans, amounting to not more than 30,000 men and 4000 cavalry, mostly Thracian. This formed all his real strength. If he had brought over in addition Persians and Indians and other Orientals, he would have found them a hindrance rather than a help. We must remember also that the Romans had a reserve to draw upon at home, but Alexander, warring on a foreign soil, would have found his army diminished by the wastage of war, as happened afterwards to Hannibal. His men were armed with round shields and long spears, the Romans had the large shield called the scutum, a better protection for the body, and the javelin, a much more effective weapon than the spear whether for hurling or thrusting. In both armies the soldiers fought in line rank by rank, but the Macedonian phalanx lacked mobility and formed a single unit; the Roman army was more elastic, made up of numerous divisions, which could easily act separately or in combination as required. Then with regard to fatigue duty, what soldier is better able to stand hard work than the Roman?
If Alexander had been worsted in one battle the war would have been over; what army could have broken the strength of Rome, when Caudium and Cannae failed to do so? Even if things had gone well with him at first, he would often have been tempted to wish that Persians and Indians and effeminate Asiatics were his foes, and would have confessed that his former wars had been waged against women, as Alexander of Epirus is reported to have said when after receiving his mortal wound he was comparing his own fortune with that of this very youth in his Asiatic campaigns. When I remember that in the first Punic war we fought at sea for twenty-four years, I think that Alexander would hardly have lived long enough to see one war through. It is quite possible, too, that as Rome and Carthage were at that time leagued together by an old-standing treaty, the same apprehensions might have led those two powerful states to take up arms against the common foe, and Alexander would have been crushed by their combined forces. Rome has had experience of a Macedonian war, not indeed when Alexander was commanding nor when the resources of Macedon were still unimpaired, but the contests against Antiochus, Philip, and Perses were fought not only without loss but even without risk. I trust that I shall not give offence when I say that, leaving out of sight the civil wars, we have never found an enemy's cavalry or infantry too much for us, when we have fought in the open field, on ground equally favourable for both sides, still less when the ground has given us an advantage. The infantry soldier, with his heavy armour and weapons, may reasonably fear the arrows of Parthian cavalry, or passes invested by the enemy, or country where supplies cannot be brought up, but he has repulsed a thousand armies more formidable than those of Alexander and his Macedonians, and will repulse them in the future if only the domestic peace and concord which we now enjoy remains undisturbed for all the years to come.
http://mcadams.posc....ivy/Livy09.html
As a background information, there had been three attempts by Greek warlords from the mainland to establish themselves in lower Italy in the 4th and 3rd century BC, all of which had initially been supported by Tarent and all of which failed: By a Spartan general in the service of Tarent, by Alexander the Molossian (334-330 BC) and by the mercurial, but brilliant Pyrrhus (280-272 BC), according to traditional historiography ranked by Hannibal himself as the second only to Alexander.
