The Persian Empire falls to Alexander the Great in 330 BCE, and he continues his march eastward through Afghanistan and into India.

Alexander defeats Porus, the Gandharan ruler of Taxila, in 326 BCE and marches on to the Ravi River before turning back.

The return march through Sindh and Balochistan ends with Alexander's death at Babylon in 323 BCE.

Greek rule does not survive in northwestern India, although a school of art known as Indo-Greek develops and influences art as far as Central Asia.

The region of Gandhara is conquered by Chandragupta (r. ca. 321-ca. 297 BCE), the founder of the Mauryan Empire, the first universal state of northern India, with its capital at present-day Patna in Bihar.

His grandson, Ashoka (r. ca. 274-ca. 236 BCE), becomes a Buddhist.

Taxila becomes a leading center of Buddhist learning.

Successors to Alexander at times control the northwestern region of present-day Pakistan and even the Punjab after Mauryan power wanes in the region.

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.)

The countries beyond “the skirts of India” are assigned to Alexander's native allies: the cities on the river Indus, with the city Patala (the capital of this part of India) are assigned to Porus; …

…those upon the Hydaspes, to Taxiles; both had been confirmed in their territories by Alexander himself.