Nikolaus Leo Overtoom provides a comprehensive study to evaluate and understand the military capabilities and accomplishments of the greatest enemy of the Seleucids and Romans, the Parthians.Overtoom draws on a wide variety of sources to reassess the militarism of the Parthians and origins and events of their first war with Rome. This book emphasizes source criticism of Greco-Roman writers to challenge traditional Rome-centric understandings of the Parthians and their military success by considering, as much as possible, the Parthians and their agency on their own terms. Through his study, the author characterizes the Parthians as capable, aggressive, and successful actors on the world stage and the role of the Romans (particularly that of the villainized Crassus) in the early stages of Parthia and Rome's rivalry is reconsidered drastically. The Parthians at War assesses broader issues of militarism and logistics, state decision-making, royal identity and ideology, imperial rivalry, propaganda, and state security concerns. Overtoom concludes that the innovations of the Parthian military were exceptional and that the realities of the origins and legacy of the first war between Parthia and Rome are significantly different from the traditional narrative.