Suetonius’ claim that Caligula had used to boast that his mother Agrippina was the result of incest between Augustus and his daughter Julia preserves a misinterpretation of his boast that he was descended from Augustus and Julia, by which he meant Julia Augusta, as Livia was known after AD14. Caligula did not mention Agrippina, or anyone else in this regard, because he assumed that his reference to his preferred account of the parentage of his grandfather Drusus would be understood by all. It was not. At some unknown date later, a hostile author misinterpreted the name of Julia Augusta in reference to Julia, Augustus’ daughter, and so misidentified the product of Augustus’ union with her as Agrippina rather than Drusus.