Marcus Vipsanius Agrippa Postumus (12 BC - 14 AD) was the son of Marcus Vipsanius Agrippa and the disgraced Julia Augusti Filia. He was therefore Augustus's grandson. Tacitus tells us that he was banished, but the reason for his exile is unclear. Tacitus hints at an antipathy between Postumus and Livia, and this is the theme that Graves picks up on. Graves's fictionalised account is an attempt to explain what history has failed to elucidate.