Contrary to the view here popularized by Cassius Dio , however , Nerva had in fact little choice with regard to his successor . Faced with a major crisis , he desperately needed the support of a man who could restore his damaged reputation . The only candidate with sufficient military experience , consular ancestry , and connections was Trajan . Likewise , Edward Gibbon 's assertion that Nerva hereby established a tradition of succession through adoption among the Five Good Emperors has found little support among modern historians .