Battle of Ipsus
In 303 BCE, Seleucus I led an army to the Indus in India, where he encountered Chandragupta. The confrontation ended with a peace treaty, and "an intermarriage agreement" (epigamia), meaning either a dynastic marriage or a more general agreement for intermarriage between Indians and Greeks. Accordingly, Seleucus ceded to Chandragupta his northwestern territories as far as Arachosia and received 500 war elephants (which played a key role in the victory of Seleucus at the Battle of Ipsus):