one of three nomadic or seminomadic tribes in the confederacy of the Dahae living east of the Caspian Sea; its members founded the Parthian empire. After the death of Alexander the Great (323 BC) the Parni apparently moved southward into the region of Parthia and perhaps eastward into Bactria. They seem to have adopted the speech of the native Parthians and been absorbed into the settled population. According to tradition Arsaces I (reigned c. 250 BC–c. 211 BC) was the first ruler of the Parthians and founder of the Parthian empire; a governor under Diodotus, king of the Bactrian Greeks, he revolted and fled westward to establish his own rule. The ruling family of the Parni in Parthia became known as the Arsacid dynasty, and Parthian kings were called Arsaces.