According to the
Puranas, Brihadratha succeeded his father
Shatadhanvan to the throne and ruled for three years.
Overthrow by Pushyamitra Shunga Brihadratha Maurya the last Mauryan Emperor was killed in 185 BCE and power usurped by his general, Pushyamitra Shunga who then took over the throne and established the Shunga Empire.
Bāṇabhaṭṭa's
Harshacharita says that Pushyamitra, while parading the entire Mauryan Army before Brihadratha on the pretext of showing him the strength of the army, crushed his master. Pushyamitra killed the former emperor in front of his military and established himself as the new ruler.
Invasion of Demetrius I In 185 BCE just after the assassination of Brihadratha by his army chief
Pushyamitra,
Greco-Bactrian king
Demetrius (Dharmamita) invaded northwestern India (parts of modern-day
Afghanistan and
Pakistan) and occupied it. The Mauryans had diplomatic alliances with the Greeks, and they may have been considered as allies by the Greco-Bactrians. A key detail is mentioned by Sri Lankan Buddhist monks in the
Paramparapustaka chronicle, pointing that Brihadratha married Demetrius' daughter, Berenice (
Suvarnnaksi in Pali language). The Greco-Bactrians may also have invaded India in order to protect Greek populations in the subcontinent. He established his rule in the Kabul Valley and parts of the
Punjab region. Soon, however, they had to leave for Bactria to fight a fierce battle (probably between
Eucratides I and Demetrius). The hypothesized
Yavana invasion of Pataliputra is based in the
Yuga Purana. The scripture describes the campaign of King Dharmamita: {{quote|{{ordered list | start = 47 == See also ==