Alexander the Great had come 2,500 miles since crossing the Hellespont in 334 bc and conquering the Persian Empire to the Indian frontier. Now, planning to attack India itself, he ordered shipwrights to prepare landing craft for use on the Hydaspes and Indus Rivers, which flanked the border. In March 326 bc, Alexander crossed the Indus and seized Taxila, establishing a base for the invasion. Here he learned that Porus, an Indian prince, was marshaling his army on the banks of the Hydaspes. Alexander marched his army 110 miles from Taxila to the Hydaspes, where Porus’ army of 30,000 infantry, 4,000 cavalry, 300 chariots and 200 elephants waited on the far bank. Alexander faced a forced river crossing opposed by a strong enemy.
Alexander’s army comprised 23,000 Greek heavy infantry, 1,000 Iranian horse-archers and 8,000 heavy cavalry. While calling up his landing craft, he sent for large supplies of wheat to persuade Porus that he would wait until the rainy season ended before crossing. For several nights Alexander marched his cavalry up and down the riverbank as if searching for a crossing point. At first Porus moved to keep him in check, but after concluding that Alexander had no intention of crossing, Porus remained in camp. Alexander’s forces now roamed the riverbank unchallenged.
Alexander divided his army into three parts. A force of 3,000 cavalry and 8,000 infantry under Craterus stayed directly opposite Porus’ position. Alexander led the turning force of 5,000 cavalry and 10,500 infantry, including 2,000 archers, while a reserve force of 1,000 cavalry and 4,500 infantry under Meleager waited for Alexander’s force to secure the far bank. One night a terrible storm arose, with rain, wind and thunder. Using the weather as a screen, Alexander moved his turning force into position 17 miles upstream.
His chosen crossing point was a headland that jutted into the river toward a wooded island, providing concealment for his landing craft. By dawn Alexander’s force had crossed the river and begun moving toward Porus’ camp.
With Alexander approaching, Porus faced a dilemma. Was this a feint or the main attack? Porus sent 2,000 of his cavalry to intercept Alexander, reserving his main force to deal with Craterus’ expected attack. Alexander destroyed the Indian cavalry and continued his advance. Porus then switched to the defensive, deploying his infantry in a line, each wing protected by only 1,000 cavalry and some elephants.
Alexander attacked Porus’ left with 4,000 cavalry and his right with 2,000 horsemen. Porus ordered the cavalry on his right to circle behind the battle line and reinforce his left, so Alexander’s 2,000 Greek cavalry simply followed them. Alexander then shifted his 1,000 horse-archers against Porus’ left while moving his heavy cavalry to envelop the Indian infantry. Porus extended his left to block the envelopment, which created a gap in his line. Alexander sent his heavy cavalry into the gap while the Greek cavalry riding behind the battle line shattered Porus’ left.
Porus rallied his troops into a phalanx to meet Alexander’s frontal infantry attack, so Alexander ordered his cavalry to encircle the packed Indian phalanx. Then his infantry and cavalry attacked in concert. Craterus soon arrived on the field with fresh troops, turning the battle into a slaughter. Eight hours later, Alexander had lost 280 cavalry and 700 Greek infantry, while Porus suffered 12,000 killed and 9,000 taken prisoner. The road to India was open.
- Seize the initiative. Prussian Field Marshal Helmuth von Moltke once said, “The offensive knows what it wants, whereas the defensive is in a state of uncertainty.”
- Conceal your intentions. Alexander deceived Porus into thinking he wouldn’t cross the Hydaspes until the dry season.
- Use darkness and weather to your advantage, as Alexander did. The Germans did the same at the Battle of the Bulge.
- Force your enemy into a tactical mistake and then exploit it. Alexander compelled Porus to extend his flank then sent his cavalry into the resulting gap.
- Know the terrain. Alexander never fought a battle without first examining the field.
- Learn from history. Napoléon studied Alexander’s campaigns. At the 1809 Battle of Wagram, he faced the same problem on the Danube that Alexander had faced on the Hydaspes and solved it the same way: Napoléon kept a pinning force across from the enemy camp, sent a turning force upstream, crossed on an island and turned the enemy flank—all in a driving rain.