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.
Roman emperor Emperor Theodosius I's sons Arcadius and Honorius succeeded as co-emperors. Eighty-five years later, following Germanic migrations which had reduced the empire's effective control across Brittania, Gaul and Hispania and a series of military coup d'état which drove Emperor Nepos out of Italy, the idea of dividing the position of emperor was formally abolished by Emperor Zeno (480). The Roman Empire survived in the east until 1453, but the marginalization of the former heartland of Italy to the empire had a profound cultural impact on the empire and the position of emperor. In 620, the official language was changed from Latin