Mithridates I of Parthia

Mithridates I conquered Media and Mesopotamia from the Seleucid Empire, capturing the cities of Ecbatana and Seleucia-on-the-Tigris. These conquests transformed Parthia from a minor kingdom into a major imperial power controlling the Iranian plateau and the Tigris-Euphrates valley.

Mithridates I adopted the Achaemenid title 'King of Kings' (Shahanshah) on his coinage and inscriptions. This act asserted Parthian legitimacy as the successor to the Persian Empire and established the ideological foundation for the Parthian Empire.

Mithridates I defeated and captured the Seleucid king Demetrius II Nicator during a campaign to reclaim the eastern provinces. Demetrius was held captive in Parthia for ten years, during which Mithridates consolidated his conquests.