Alexander, crossing the Indus near Attock in spring 326, …

…enters prosperous Taxila, whose ruler, Taksilla, furnishes elephants and troops in return for aid against his rival Porus, who rules the lands between the Hydaspes (modern Jhelum) and the Acesines (modern Chenab) rivers.

Porus, unlike his neighbor, Ambhi, the king of Taxila (Taksasila), resists Alexander.

In June, 326, Alexander, faced with a crossing of the Hydaspes (now called Jhetum) River in full flood and hostile Indians, supported by two hundred horse-crazing elephants, on the far side, begins to launch boats and rafts, gather up supplies, and run cavalry exercises.

When he senses the Indians growing lax, he takes across a force of eleven thousand men, leaving the main body encamped.

Employing brilliant tactics, he first employs his mobile cavalry and mounted archers to defeat the Indian chariots, then destroys the bunched, slow-moving infantry, setting his own infantry against the elephants with axes.

Seleucus, the son of Antiochus, a general of Philip, has participated in the conquest of the Persian empire as one of Alexander's officers, and commands the Macedonian infantry in the battle.

Alexander founds two cities on the left bank of the Hydaspes, Alexandria Nicaea (to celebrate his victory) and Bucephala (named after his horse Bucephalus, which dies there).

Impressed by Porus' techniques and spirit, Alexander allows him to retain his kingdom and perhaps even cedes some conquered areas to him.

(Not known in Indian sources, the name Porus has been conjecturally interpreted as standing for Paurava; i.e., the ruler of the Purus, a tribe known in that region from ancient Hindu Vedic times.)