Philip's Army, Alexander's War

Military History: Alexander the Great

Chapter 1 · Introduction: Picking Up From Philip II's Reforms

In thirteen years, from 336 to 323 BCE, Alexander III of Macedon led an army from northern Greece to the Indus valley and destroyed the largest empire the world had yet seen. This course follows those campaigns as military history: the army, the battles, the sieges, and the decisions behind them. It begins where Military History: The Greeks, Chapter 9, deliberately stopped — with the army Philip II built.

Where This Course Fits

Course	What it covers
Military History: The Greeks, Chapter 9	Philip II's reforms, the sarissa phalanx, and the Battle of Chaeronea (338 BCE)
This course	Alexander's own campaigns, from his accession in 336 BCE to his death in 323 BCE, and the immediate military aftermath
Greek & Roman History, Chapter 5	The political story after Alexander: his successors and the Hellenistic kingdoms

The Army Alexander Inherited

Alexander didn't build his army; his father did. What Alexander added was the skill to use it in almost every kind of war — open battle, siege, mountain fighting, and counter-guerrilla campaigns.

The Phalanx (Pezhetairoi)

Heavy infantry carrying the sarissa, a two-handed pike up to about 6 metres long. Its job was to hold and pin the enemy's centre.

The Hypaspists

Elite, more flexible infantry who linked the phalanx to the cavalry and were often used for the hardest tasks, such as storming walls.

The Companion Cavalry

Macedonian noble heavy cavalry, usually led by Alexander himself, charging in a wedge formation. This was the army's striking arm — as Alexander showed leading it at Chaeronea, aged eighteen.

Allies and Specialists

Thessalian cavalry, Greek allied infantry, Agrianian javelin-men, Cretan archers, and engineers who built siege towers and catapults.

Combined Arms The key idea, already present under Philip, was that each part had a job: the phalanx held, light troops screened, and the cavalry delivered the decisive blow, often into a gap the enemy's own movement had created. Watch for this pattern at the Granicus, Issus, and Gaugamela.

The War Philip Planned

338 BCE Victory at Chaeronea leaves Macedon the dominant power in Greece.
337 BCE The League of Corinth, an alliance of Greek states, names Philip its leader for a war against Persia — officially revenge for the Persian invasions of Greece 150 years earlier.
336 BCE An advance force under the generals Parmenion and Attalus crosses into Asia Minor. That summer Philip is assassinated, and Alexander, aged twenty, becomes king (Chapter 2).
334 BCE Alexander crosses the Hellespont with around 32,000 infantry and 5,000 cavalry, joining the advance force (Chapter 3).

The Enemy: The Achaemenid Empire

Persia's empire stretched from the Aegean to the Indus and from Egypt to Central Asia, divided into provinces run by governors called satraps. It could raise far larger armies than Macedon and had huge wealth.

Darius III

Became king in 336 BCE, the same year as Alexander. His armies included excellent cavalry and thousands of Greek mercenaries, such as those led by Memnon of Rhodes.

How Do We Know? The Source Problem

Several men who marched with Alexander wrote accounts of the campaigns, including his official historian Callisthenes, his general Ptolemy (later king of Egypt), the officer Aristobulus, and the admiral Nearchus. None of their works survives. What we have are later writers who used them.

Surviving source	Written	Mainly based on
Diodorus Siculus, Book 17	1st century BCE	Cleitarchus, who wasn't an eyewitness
Quintus Curtius Rufus	1st century CE (two of ten books lost)	Largely Cleitarchus, some Ptolemy
Plutarch, Life of Alexander	Around 100 CE	Many sources; more interested in character than tactics
Arrian, Anabasis	2nd century CE	Ptolemy and Aristobulus, both eyewitnesses
Justin	Uncertain	A short summary of an earlier lost history by Trogus

Read Every Number With Care Our best source, Arrian, wrote more than four centuries after the events, and his main source, Ptolemy, had good reasons to make himself and Alexander look good. The other main tradition, often called the "vulgate," comes largely from Cleitarchus and includes more dramatic stories. Ancient figures for Persian army sizes are often hundreds of thousands, far beyond what modern historians think possible. This course gives the ancient figures where useful, but flags them.

A Familiar Problem Every course in the Military History sub-series has had to separate the popular story from what the evidence supports. Alexander is the extreme case: he became a legend within his own lifetime, and the legend has shaped almost everything written about him since.

The Course at a Glance

336–335 BCE Securing Macedon and Greece; the destruction of Thebes (Chapter 2)
334 BCE The Granicus (Chapter 3)
333 BCE Issus (Chapter 4)
332 BCE The Siege of Tyre (Chapter 5); Egypt (Chapter 6)
331 BCE Gaugamela (Chapter 7)
330–325 BCE Bactria, Sogdiana, and India (Chapter 8)
323 BCE Death in Babylon (Chapter 10)

Questions to Sit With

How much credit for Alexander's victories belongs to Philip, who built the army?

If the eyewitness accounts are all lost, how far can we trust any detailed description of Alexander's battles?

Why might a war "for revenge" on Persia have been useful to Philip politically, whatever his real aims?

Quick Reference — Chapter 1

Alexander's campaigns ran from 336 to 323 BCE, from Macedon to the Indus
He inherited Philip II's army: the sarissa phalanx, hypaspists, Companion cavalry, and allied and specialist troops working as a combined-arms system
The League of Corinth (337 BCE) named Philip leader of a war on Persia; an advance force crossed in 336 BCE; Alexander crossed in 334 BCE with about 32,000 infantry and 5,000 cavalry
The enemy was the Achaemenid Persian Empire under Darius III, also king from 336 BCE
All eyewitness accounts are lost; the main surviving sources are Arrian (based on Ptolemy and Aristobulus) and the "vulgate" tradition (Diodorus, Curtius, Justin), with Plutarch alongside

What's Next

Chapter 2: Alexander's Succession & the Real Consolidation of Macedon.