The Greek author Plutarch of Chaeronea gives the following assessment of Alexander the Great in his treatise on Alexander's fortune and virtue (328c-329d): he brought civilization to Asia. Many historians have believed that these words are historically accurate, although they are taken from a laudatory speech.
The translation was made by M.M. Austin.
An ancient assessment of Alexander
 If you consider the effects of Alexander's instruction, you will see that he educated the Hyrcanians to contract marriages, taught the Arachosians to till the soil,note[A preposterous remark. The word Arachosia means "well-watered land" and indicates the high quality of its agriculture.] and persuaded the Sogdians to support their parents, not to kill them,note[The Greeks believed that there were cannibals in Central-Asia.] and the Persians to respect their mothers, not to marry them.note[So much for Greek understanding of polygamy.] Most admirable philosophy, which induced the Indians to worship Greek gods, and the Scythians to bury their dead and not to eat them!
We admire the power of [the Athenian philosopher] Carneades, who caused Clitomachus, formerly called Hasdrubal and a Carthaginian by birth, to adopt Greek ways. We admire the character of Zeno, who persuaded Diogenes the Babylonian to turn to philosophy. Yet when Alexander was taming Asia, [the legendary poet] Homer became widely read, and the children of the Persians, of the Susianians and the Gedrosians sang the tragedies of Euripides and Sophocles.
And Socrates was condemned by the sycophants in Athens for introducing new deities, while thanks to Alexander Bactria and the Caucasus worshipped the gods of the Greeks. Plato drew up in writing one ideal constitution but could not persuade anyone to adopt it because of its severity, while Alexander founded over seventy cities among barbarian tribes, sprinkled Greek institutions all over Asia, and so overcame its wild and savage manner of living. Few of us read Plato's Laws, but the laws of Alexander have been and are still used by millions of men.
Those who were subdued by Alexander are more fortunate than those who escaped him, for the latter had no one to rescue them from their wretched life, while the victorious Alexander compelled the former to enjoy a better existence. [...] Alexander's victims would not have been civilized if they had not been defeated. Egypt would not have had its Alexandria, nor Mesopotamia its Seleucia, nor Sogdia its Prophthasia, nor India its Bucephalia, nor the Caucasusnote[Here you can read more about Alexander's founding of Alexandria. Seleucia was in fact founded by Seleucus, the first of the Seleucid kings. Prophthasia was not situated in Sogdia, but in Drangiana. Bucephalia was built on the banks of the Hydaspes. The last town mentioned is Alexandria in the Caucasus, Chârikâr in the Hindu Kush, 75 kilometers north of modern Kabul.] a Greek city nearby; their foundation extinguished barbarism, and custom changed the worse into better.
If, therefore, philosophers take the greatest pride in taming and correcting the fierce and untutored elements of men's character, and if Alexander has been shown to have changed the brutish customs of countless nations, then it would be justifiable to regard him as a very great philosopher.
 Furthermore, the much-admired Republic of Zeno, the founder of the Stoic school, is built around one guiding principle: we should not live in separate cities and villages, each using its own rules of justice, but we should consider all men to be fellow-villagers and citizens, with one common life and order for all, like a flock feeding together in a common pasture. This Zeno wrote, conjuring up as it were a dream or an image of a well-ordered and philosophic constitution, but it was Alexander who turned this idea into reality. For he did not follow the advice of Aristotle and treat the Greeks as a leader would but the barbarians as a master, nor did he show care for the Greeks as friends and kinsmen, while treating the others as animals or plants; this would have filled his realm with many wars and exiles and festering unrest. Rather, believing that he had come as a god-sent governor and mediator of the whole world, he overcame by arms those he could not bring over by persuasion and brought men together from all over the world, mixing together, as it were, in a loving-cup their lives, customs, marriages and ways of living.
He instructed all men to consider the inhabited world to be their native land, and his camp to be their acropolis and their defense, while they should regard as kinsmen all good men, and the wicked as strangers. The difference between Greeks and barbarians was not a matter of cloak or shield, or of a dagger or Median dress. What distinguished Greekness was excellence, while wickedness was the mark of the barbarian; clothing, food, marriage and way of life they should all regard as common, being blended together by ties of blood and the bearing of children.