If you can’t tell Nero from Caligula, if you’ve never heard of Elagabalus or Antoninus Pius, Mary Beard wants to reassure you. A lot of people living in the Roman empire didn’t know the names of their emperors either. “Most Romans in Britain didn’t know who was on the throne,” she says. “They knew an emperor was on the throne. But if you say Nero, they’d say ‘Who?’” The Roman empire was a remarkably stable institution, and the role and indeed the iconography of the emperor remained basically the same for more than two hundred years. Beard’s fascinating new book...