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 Sejanus had the priests and magistrates add prayers for the health of Nero and Drusus in addition to those normally offered to the emperor on that day. Tiberius was not happy with this and he voiced his displeasure in the Senate. In addition, he questioned the priests of the Palatine. Some of the priests who offered the prayers were relatives of Agrippina and Germanicus. This made Tiberius suspicious of her and marked a change in his attitude toward her and her older sons, but not Caligula. In AD 25, Sejanus requested Livilla's hand in marriage. Livilla was a niece of