This article is a study of the fi rst years of the rule of Ardasheer Papakan, the founder of the Sasanian dynasty in Iran, up to the downfall of the Parthian state. An examination of the sources suggests that the chronology of Ardasheer's rule should be revised. Ardasheer appears to have ruled as King of Kings in 225, when he destroyed the Parthians, through the fi rst months of 241. His victory in the bitter fi ght for power was due to a number of factors which included, in addition to his own abilities, the support which he increasingly gained among the noblemen.