The Parthian Empire was a major Iranian political and cultural power in ancient Iran. Arsaces I of Parthia, a leader of the Parni tribe, founded the country in the mid-3rd century BC when he conquered the region of Parthia in Iran's northeast, then a province in rebellion against the Seleucid Empire. Mithridates I of Parthia greatly expanded the empire by seizing Media and Mesopotamia from the Seleucids. At its height, the Parthian Empire stretched from the northern reaches of the Euphrates, in ...