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.
Emperor Yang of Sui Emperor Yang had Li Hun, Li Min, and their clansmen executed, and further poisoned Yang Lihua's daughter Yuwen Eying (宇文娥英). Later in 615, Emperor Yang carried out a tour of the northern provinces with the Empress Xiao and much of the imperial court. Shibi Khan, angered that the imperial advisor Pei Ju had promised a princess to his brother Ashina Chiji () and had executed his close advisor Shishu Huxi () under false pretenses, launched a surprise attack on Yanmen Commandery. In accordance with Turkish customs, Princess Yicheng had married him as her husband's successor; having been well treated by