The surviving histories speak equally positively of Nerva 's brief reign , although none offer a substantial commentary on his policies . Both Cassius Dio and Aurelius Victor emphasize his wisdom and moderation , with Dio commending his decision to adopt Trajan as his heir . These views were later popularized by the 18th @-@ century historian Edward Gibbon in his History of the Decline and Fall of the Roman Empire . Gibbon considered Nerva the first of the Five Good Emperors , five successive rulers under whom the Roman Empire " was governed by absolute power , under the guidance of wisdom and virtue " from 96 until 180 . Nevertheless , even Gibbon notes that , compared to his successors , Nerva may have lacked the necessary qualifications for a successful reign :