Alexander the Great entered the borders of India in 327 BC with his army hoping to conquer the great country that had been a legend to the Greeks since at least the time of Herodotos. The Makedonians found India and the Indians to be far less supernatural than they had been led to expect, although the land was very wealthy and the people ready for war. Despite some victories and a favorable alliance with the powerful king, Poros (Parvataka or Parvatesha), India at last broke the formerly undefeated Makedonian army. Alexander would have pushed further into the subcontinent beyond the Punjab but in 325 BC his weary troops, fearful of the rumors of the strong king of Magadha, mutinied on the bank of the river Hyphasis. The Makedonian king was forced to return west with India largely unconquered.

Alexander left behind agents in order to control the territories that he had overrun and to maintain the alliance with Poros who quickly abused their authority. With the treaty broken thus, Poros joined the cause of Chandragupta (Sandrakottos) Maurya, a powerful king who defeated the great Nanda king of Magdha in 323 - 322 BC. Together they overthrew the remaining Makedonians and lay the foundation for what would become one of the largest empires to ever exist in India. By the time Seleukos I Nikator made his own attempt to annex India in 305 BC, the Mauryan Empire of Chandragupta encompassed most of modern Pakistan and India north of the Vindhya mountain range.

Chandragupta met Seleukos in battle somewhere in Gandhara and defeated the forces of the successor king. A treaty was made between the two rulers in which Seleukos ceded authority over the eastern satrapies of Aria, Arachosia, Gedrosia and the Paropanisadai and Chandragupta gave Seleukos a gift of 500 war elephants. These animals were instrumental in the defeat of Antigonos Monophthalmos in 301 BC. Chandragupta also recieved the hand of a daughter of Seleukos. The kings parted on good terms with Seleukos maintaining an ambassador named Megasthanes at the Mauryan court in Pataliputra.