Incest of unequal gravity: the "incestus iuris gentium," which was applied to both Romans and non-Romans in the Empire, and the "incestus iuris civilis," which concerned only Roman citizens. Therefore, for example, an Egyptian could marry an aunt, but a Roman could not. Despite the act of incest being unacceptable within the Roman Empire, Roman Emperor Caligula is rumored to have had sexual relationships with all three of his sisters (Julia Livilla, Drusilla, and Agrippina the Younger). Emperor Claudius, after executing his previous wife, married his brother's daughter Agrippina the Younger, and changed the law to allow an otherwise illegal union.
Agrippina the Younger whereupon he replied "I don't think anything produced by me and Agrippina could possibly be good for the state or the people". Caligula and his sisters were accused of having incestuous relationships. On June 10, AD 38, Drusilla died, possibly of a fever, rampant in Rome at the time. He was particularly fond of Drusilla, claiming to treat her as he would his own wife, even though Drusilla had a husband. Following her death Caligula showed no special love or respect toward the surviving sisters and was said to have gone insane. In 39, Agrippina and Livilla, with their maternal