Alexander III, acceding at age twenty to the throne of Macedon in 336 BCE, had set his mind on the Persian invasion conceived by his father Philip, having grown up to the idea.

Moreover, he needs the wealth of Persia if he is to maintain the army built by Philip and pay off the five hundred talents he owes.

The exploits of the Ten Thousand, Greek soldiers of fortune, and of Agesilaus of Sparta, in successfully campaigning in Persian territory have revealed the vulnerability of the Persian Empire.

With a good cavalry force, Alexander can expect to defeat any Persian army.

Having secured his base in Greece, Alexander sets out for Asia in spring 334 BCE.

He leaves behind his sixty-three-year-old general Antipater, who has already faithfully served his father, as governor of Greece, with twelve thousand foot soldiers and fifteen hundred cavalry, while taking with him between thirty thousand and forty thousand foot soldiers (twelve thousand of them Macedonians) and more than six thousand cavalry.

To what extent Alexander had needed to reorganize the army at the outset of the expedition is unclear.

Whereas Greek armies expect to live off the land to some extent, Alexander uses wagons, despite a tradition that his father Philip II had forced his soldiers to carry their own provisions and equipment.

This army is to prove remarkable for its balanced combination of arms.

Much work will fall on the lightly armed Cretan and Macedonian archers, Thracians, and the Agrianian javelin men, but the core of the infantry is the Macedonian phalanx, nine thousand strong, armed with the thirteen-foot long sarissa, or spear.

In pitched battle, the striking force is the cavalry, and the pick of the cavalry are the Companions, led by Alexander himself on the right wing.

Philip's great general Parmenio, who had secured a foothold in Asia Minor during Philip's lifetime, commands the Thessalian cavalry on the left; many of the sixty-four-year-old warrior's family and supporters are entrenched in positions of responsibility.

In addition, there are lighter armed troops, such as the scouts, and less-coordinated but highly effective contingents of slingers and other irregulars, usually from the parts of Greece where the concept of polis is imperfectly developed.

This army is a formidable machine in the metaphorical sense.

There also are literal machines-stone-throwing siege engines that can be assembled on the spot.

The Thessalian siege engineers associated with Philip certainly continue into Alexander's reign (and will enable him to conquer Anatolia and Phoenicia at comparatively high speed, given the fortified obstacles confronting him).

Surveyors, engineers, architects, scientists, court officials, and historians accompany the army of Alexander, who, from the outset, seems to envisage an unlimited operation.

Callisthenes, a nephew and former student of Aristotle, is appointed to attend Alexander as historian on his uncle's recommendation.

He will write a history of Greece from the peace of Antalcidas (386 BCE) to the Phocian War (355 BCE), a history of the Phocian War, and other works in addition to his account of the Asiatic campaign (all of which have perished).

His account of Alexander's expedition will be preserved long enough to be mined as a direct or indirect source for other histories that have survived; Polybius will scold Callisthenes for his poor descriptions of the battles of Alexander.

Alexander III of Macedon, leading some thirty thousand infantry and five thousand cavalry, invades Asia Minor in 334 in fulfillment of his father’s dream of punishing Persia for the Greco-Persian Wars and for its dominance thereafter of the Balkan Peninsula.

As soon as Alexander crosses the Hellespont, he casts his spear into Asian soil and openly declares that he lays claim to all Asia, which is at this time a fluid geographical concept.

In a romantic gesture inspired by Homer, he visits Troy, paying due religious honor to the tombs of the heroes Achilles and Ajax.

He now marches on Phrygia, where Darius III, the Achaemenid king of Persia, waits with an army.

Alexander confronts his first Persian army at the Granicus River (modern Kocabas, flowing into the Sea of Marmara) in May/June 334.

This is not the central army of the Persian king but a very sizable force levied by the satraps from Anatolia itself, numbering perhaps forty thousand and led by three satraps.

Darius has made no serious preparations to resist the Macedonian invasion.

Alexander's shock troops ford the stream and clamber up the bank under a shower of javelins.

Alexander follows and charges the generals, who are concentrated in the left center of the Persian line, leading the right wing with a battle cry to the god of battle.

He kills two relatives of the Persian king, Darius, and is himself saved from death by his cavalry commander, Cleitus the Black.

The Persian plan to tempt Alexander across the river and kill him in the melee almost succeeds; but the Persian line breaks, and Alexander's victory is complete.

Darius' Greek mercenaries are largely massacred, but two thousand survivors are sent back to Macedonia in chains.

According to Alexander's biographer, Arrian (second century CE), the struggle has cost the Macedonians only one hundred and fifteen men.

This victory exposes western Asia Minor to the Macedonians, and most cities hasten to open their gates.

The tyrants are expelled and (in contrast to Macedonian policy in Greece) democracies are installed.

Alexander thus underlines his Panhellenic policy, already symbolized in the sending of three hundred panoplies (sets of armor) taken at the Granicus as an offering dedicated to Athena at Athens by “Alexander son of Philip and the Greeks (except the Spartans) from the barbarians who inhabit Asia.” (This formula, cited by the Greek historian Arrian in his history of Alexander's campaigns, is noteworthy for its omission of any reference to Macedonia.)

However, the cities remain de facto under Alexander, and his appointment of Calas as satrap of Hellespontine Phrygia reflects his claim to succeed the Great King of Persia.

Ephesus submits to Alexander in 334 BCE, but when …

…Miletus, encouraged by the proximity of the Persian fleet, resists, Alexander takes the city in mid-334 by assault.

Refusing a naval battle, he disbands his own costly navy and announces that he will “defeat the Persian fleet on land,” by occupying the coastal cities to deprive the Persian fleet of its ports.

Whether the Greek cities of Anatolia now join the League of Corinth is an intractable question.

Some of the islanders certainly do, as, for instance, Chios, where an inscription recording the terms of Alexander's settlement proclaims bluntly, “the constitution is to be a democracy” and refers to the “decrees of the Greeks.”

As for Asiatic cities like Priene, there is no certainty, but the probability is that they join the league.

As a gift to the new city, Alexander himself dedicates its main temple, of Athena Polias, built by Pythius, probable architect of the Mausoleum of Halicarnassus and author of a theoretical book on architecture.

Pythius, like other architects and sculptors of the time, employs strict canons of proportion in designing the small rebuilt temple.