Due to the lack of written sources on this period , much of Nerva 's life has remained obscure . The most substantial surviving account of the reign of Nerva was written by the 3rd @-@ century historian Cassius Dio . His Roman History , which spans nearly a millennium , from the arrival of Aeneas in Italy until the year 229 , was composed more than one hundred years after Nerva had died . Further details are added by an abridged biography from the Epitome de Caesaribus , a work alleged to have been authored by the 4th @-@ century historian Aurelius Victor .