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 Elder still survives (). Agrippina was fiercely independent, a trait she shared with her mother. Dio described her as having ambitions to match her pedigree. However, Anthony Barrett notes that Agrippina was fully aware that a woman in ancient Rome could not hold power in her own right. Instead, Agrippina followed the model of Livia in promoting the careers of her children. She and her daughter, Agrippina the Younger, are both described as being equally ambitious for their sons. Whereas the elder Agrippina's son failed to become emperor, the younger Agrippina's son, also named Nero, succeeds. In a contrast, Tacitus has