Arsaces (är´səsēz), fl. 250 BC, founder of the Parthian dynasty of the Arsacids, which ruled Persia from c.250 BC to AD 226. Arsaces led a successful revolt against Antiochus II of Syria, when Antiochus was engaged in war with Egypt and trying to put down a revolt in Bactria. Among the other Parthian kings were Tiridates, Mithradates I, Mithradates II, and Phraates IV. Their empire became a formidable rival of the Roman power, but began to decay in the 2d cent. AD after Emperor Alexander Severus had invaded the country. The Arsacids were overthrown by a revolt of the Persians under Ardashir I, who in AD 226 slew Artabanus IV (Ardawan IV), the last of the Arsacids.