Agrippina the Younger
The Romans, unlike the Egyptians, frowned upon incest, regarding it as nefas “against divine law.” No Roman was supposed to marry or have sex with anyone closer than a cousin- although concessions were made later for provincials such as the Egyptians. However, incest was never acceptable for any respectable Roman- unless you happened to be a member of the imperial family. Julia Agrippina or Agrippina the Younger was the sister, niece, and mother of emperors. She is also reputed to have had sexual relations with her brother and son- and married her uncle.
Agrippina was born into a complicated family, the Julio-Claudians. Her great Uncle Tiberius exiled her mother, Agrippina, the Elder, and her father, Germanicus, a general and brother of the future emperor Claudius, died when she was a child. In 37AD, Agrippina’s brother, Caligula became emperor.
Bad or mad, Caligula reputedly had sexual relations with all three of his sisters. The unprecedented honors he awarded them and his known depravity make it likely. Caligula gave his sisters the same rights of the Vestal Virgins. They appeared on the same coins as Caligula, and he added their names to loyalty oaths sworn to him
After Caligula’s death, Agrippina’s uncle, Claudius, became Emperor. After Claudius executed his wife, Messalina for treason and adultery, the race was on to find a suitable replacement. The palace freedman, Narcissus proposed Agrippina as a likely match -despite the fact she was the emperor’s niece. Claudius agreed and changed the law so that he could marry his brother’s daughter and so the marriage went ahead.
The only love or lust involved in the relationship between Uncle and niece was that of power; it is debatable whether the couple ever consummated their union. However, as far as the Roman populace was concerned, it was incest and so won widespread public disapproval.
Claudius made Agrippina’s son, Lucius Domitius Ahenobarbus, later Emperor Nero, his principal heir. Suetonius describes how Nero felt a lecherous passion for his mother but, unable to consummate it; he found a mistress, Acte, who was her very image. However, as soon as Agrippina discovered her grip on Nero slipping, she reputedly gave in and slept with her son.
Suetonius claimed when the couple traveled together in a closed litter; the emperor often emerged with ‘stains’ on his clothing. Tacitus also insinuates that Agrippina offered her son sex to control him- until he murdered her in AD 59.