The battle of the Hydaspes River was a tactical masterstroke, Alexander the Great, outflanking the superior Indian force and inflicting a severe defeat on his enemy in 326 BCE.
Alexander's ambitions drew him ever eastwards, adding new territories to his empire as he went. His force of veteran infantry and cavalry was becoming increasingly war-weary as they approached India. They had defeated every foe they encountered, but were deep in unfamiliar territory and facing a well-organized and equipped army under the command of King Porus.
Alexander Crosses The Hydaspes
Porus chose to take up a defensive position behind the Hydaspes River. He did not need to defeat Alexander decisively, only to keep him out of his territory. His intent was to prevent a crossing of the Hydaspes, which would be entirely sufficient to achieve his strategic aims. He was also operating at the end of a shorter supply line than alexander and could afford to outwait his opponent.
Never one for inaction even if he could afford to remain static, Alexander ordered part of his army to demonstrate across the river from Porus while the majority made a crossing upstream. A thunderstorm helped conceal the movement, allowing Alexander to assemble his force and begin marching along the riverbank.
Knowing that his cavalry could not face Porus' war elephants, Alexander sent the majority of it against Porus' left flank, drawing reinforcements to the area. The Macedonian phalanx advanced against Porus' elephants, using their long pikes to good effect. The elephants were driven into the Indian infantry and created severe disorder.
The remainder of Alexander's cavalry, which had made a flank march, attacked Porus' left flank cavalry in the rear. Meanwhile, the Macedonian forces left on the far bank began to cross the river and join the fight. The Indian army, which had fought stubbornly, eventually collapsed.
King Porus himself was captured, but so impressed was Alexander with his conduct that he returned Porus to power as a client of Alexander's empire in much the same way that Alexander had installed some of his generals as rulers of conquered areas.
The weary Macedonian army demanded a return home soon afterward, and Alexander was forced to concede, bringing his great campaign of conquest to an end. Battle Of Gaugamela: Alexander The Great Leads 47,000 Troops To Victors Against 240,000 Persians