Good question. Our Roman sources say nothing about Nerva before he became emperor except that he was old and had been to more orgies than any living man left in Rome. Somehow Domitian hadn't got round to killing him to make a vacancy in the post room so Nerva had carried on unmolested. Besides licking stamps (his story at least), Nerva took time out to sleep in the Senate. He was well-liked although why that was we simply don't know. Theories include that he had a great sense of humour, that he put men at ease with his cheeky winking and that he was a veteran of the carnal arts and, indeed, the Carnival of Arse.