The site lay near the Tigris river, on firm level earth suitable for chariots and horsemen.
Persian engineers reportedly cleared and smoothed the terrain for miles around.
They wanted nothing to disrupt the charge of the famous scythed chariots.
On paper, the plan made sense, and the advantage seemed overwhelming.
Before describing the battle, look closely at the two armies which faced each other.
Alexander commanded perhaps forty thousand infantry and seven thousand cavalry.
Exact numbers are debated, but all sources agree he was significantly outnumbered.
At the heart of his force stood the Macedonian phalanx, six battle hardened infantry battalions.
Each phalangite carried a long pike called the sarissa, often around five or six meters.
These pikes projected several ranks deep beyond the front line of soldiers.
The formation produced a bristling hedge of spear points difficult for enemies to penetrate.
Phalangites wore armor and carried small shields, relying on tight formation for protection.
They were not particularly flexible in broken ground but devastating on level terrain.
Supporting the phalanx were elite infantry such as the Hypaspists, the so called shield bearers.
These men fought with shorter spears and larger shields, giving them greater mobility.
They usually guarded the crucial junction between phalanx and cavalry wing.
Alexander also deployed experienced Greek mercenary hoplites, accustomed to disciplined combat.
On his flanks he placed a mix of Greek, Thracian, and other light infantry.
These troops were skilled with javelins, slings, and bows, useful against cavalry and chariots.
Alexander’s true striking power lay in his cavalry, especially the Companion cavalry.
These were heavy horsemen recruited from Macedonian nobility and trained from youth.
They wore armor, carried long lances, and specialized in wedge shaped shock charges.
Alexander personally commanded the right wing Companion squadrons, his favorite instrument of decision.
On his left, the cavalry was commanded by Parmenion, an older experienced general.
This wing contained Thessalian cavalry, respected for discipline and skill.
Together, Macedonian arms combined a solid infantry center with hard hitting mobile wings.
Alexander’s army was also closely coordinated and accustomed to his leadership style.
He issued clear tactical roles, and his officers understood his preference for aggressive maneuver.
Opposite them, Darius commanded a much larger but more heterogeneous force.
Ancient sources offer wildly inflated Persian numbers, sometimes hundreds of thousands.
Modern estimates suggest perhaps forty to fifty thousand infantry and thirty to forty thousand cavalry.
Darius also fielded scythed chariots, perhaps around two hundred in total.
Some accounts mention a few early war elephants, though their battlefield influence was limited.
The Persian infantry included royal guards known as the Apple Bearers because of their spear pommels.
These men fought near the king, forming an elite core of defense.
There were also Persian and Median infantry, plus contingents from many subject peoples.
Their equipment and fighting styles varied widely, making coordinated maneuvers difficult.
The Persian strength lay above all in cavalry, particularly eastern Iranian horse archers and lancers.
These riders came from regions like Bactria, Sogdiana, and other eastern satrapies.
They were fast, numerous, and dangerous on open ground where they could surround enemies.
The scythed chariots were intended as terror weapons against dense infantry formations.
Each chariot carried blades fixed to the axle, projecting beside the wheels.
When driven at speed into a compact mass of infantry, they could rip open lanes.
Success depended on level ground and lightly protected enemy soldiers.
Darius placed great faith in these chariots and prepared the battlefield accordingly.
The night before the battle, the two armies camped within sight of each other.
Persian forces reportedly kept torches burning and noise echoing through the darkness.
Alexander convened his council and, according to some accounts, delayed until daylight.
He wanted his men rested and the terrain clearly visible before the clash.
At dawn, he formed his army in a distinctive double line.
The front line contained his fighting units, ready for engagement.
Behind them stood a second line facing outward to guard against encirclement.
He understood that the Persians would attempt to envelop his smaller army.
By preparing a refused rear line, he reduced the risk of catastrophic flanking attacks.
Alexander placed his phalanx in the center, with Hypaspists on its right end.
He took command of the right wing cavalry, composed of Companions and supporting units.
Parmenion controlled the left wing with Thessalian horse and allied contingents.
Light infantry screened the front, ready to deal with chariots and skirmishers.
On the Persian side, Darius placed himself in the center in a high chariot.
Around him stood his elite guard infantry and chosen cavalry contingents.
On both wings he massed cavalry, intending to stretch and envelop the Macedonian flanks.
The scythed chariots rested in front of the main line, waiting for a gap.
The stage was set for a confrontation shaped by terrain, numbers, and tactical insight.
When the sun rose higher, Alexander advanced not straight ahead but on an angled line.
His right wing advanced obliquely toward the Persian left, moving diagonally across the plain.
This maneuver had several purposes that reveal his understanding of the field.
First, by moving right, he drew part of the Persian line away from prepared ground.
Persian engineers had flattened the central area for chariots and mass cavalry.
By shifting the fight toward the flank, Alexander hoped to find less favorable terrain for them.
Second, this diagonal advance forced Darius to react and spread his line wider.
To avoid being outflanked on his own left, Darius extended that wing further outward.
The Persian infantry and cavalry had to stretch to maintain contact with the Macedonians.
The more they extended, the thinner their line became at crucial points.
Third, the oblique movement created small gaps and misalignments in the Persian formations.
Alexander intended to spot or create a weak point near the Persian center left junction.
There, he hoped to drive in his Companion cavalry at the decisive moment.
Darius responded by ordering his own cavalry to move outward and engage the Macedonian right.
The battlefield slowly turned into a crescent of Persian horsemen stretching around Alexander’s flanks.
Meanwhile, in the center, the scythed chariots launched their long anticipated charge.
The chariots hurtled forward with speed, metal blades whirling at axle height.
Their target was the Macedonian phalanx, whose dense files invited such an attack.
Yet Alexander had prepared his infantry for this exact threat.
Light troops and skirmishers moved out in front of the phalanx as the chariots approached.
They hurled javelins and stones, targeted the horses, and disrupted the drivers.
Many chariots veered off course, crashed, or halted before reaching the main line.
