Founded and ruled by the Arsacid royal family, the Parthian empire (c. 250 bce–227 ce) was the native Iranian empire that filled the power vacuum in the Middle East in the midst of Seleucid decline. Arsacid interaction with the Roman empire began in the mid-90s bce, eventually established the Euphrates river as a shared border, and was peaceful in nature till 54 bce. In that year, the first of four cycles of Parthian-Roman wars began. Since the Romans carried out the initial large-scale mobilization of troops that introduced most of these wars, it is appropriate to associate these four cycles with the various Romans who coordinated the Roman military efforts: (a) Crassus to Antony (54–30 bce); (b) Nero (57–63 ce); (c) Trajan (114–117 ce); and (d) Lucius Verus to Macrinus (161–217 ce). The fundamental causes for these conflicts were Roman imperialism, which was well ingrained by the 1st century bce, and Parthian imperialism, which accelerated in the 2nd century bce, probably accompanied by the Arsacids’ attempts to present themselves as successors to the Achaemenid dynasty.