1The article takes into consideration the Parthian war of Lucis Verus and in particular, it examines the causes of the conflict. In the scarce information provided by the sources, the Parthian Great King Vologases III is described as the only one responsible for the war: his attack on Roman territory and his expansionist policy triggered by the change of power in Rome have been considered by ancient and modern authors as well, the only reason for that conflict. Hartmann challenges the traditional view maintaining that the Arsacid military initiatives perceived by Rome as aggression, that is to say, the occupation of Armenia and Osrhoene were in fact events pertaining to the sphere of Parthian internal policy. Vologases III, the first member of the new Arsacid dynasty, who gained power in 147 AD had to secure his position by placing at the head of the vassal kingdoms kings chosen by him and therefore loyal to his branch of the Arsacids. That was a sort of mandatory move he already employed in Mesene (151 AD). His actions were not meant to be a threat to Roman authority in the East or Roman territory. The defeats the Roman legati suffered at the hands of the Parthians, took place beyond Roman borders when the imperial envoys tried to use their military power to reinstall the deposed friendly kings. The unexpected defeats of both Severianus and Cornelianus provoked an escalation in the war and urged for a direct intervention of one of Rome’s co-rulers.