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.
Otto III, Holy Roman Emperor never married and never fathered any children due to his early death. At the time of his death, the Byzantine princess Zoe, second daughter of Emperor Constantine VIII was traveling to Italy to marry him. Otto III, Holy Roman Emperor Otto III (June/July 980 – 23 January 1002) was Holy Roman Emperor from 996 until his early death in 1002. A member of the Ottonian dynasty, Otto III was the only son of the Emperor Otto II and his wife Theophanu. Otto III was crowned as King of Germany in 983 at the age of three, shortly after his father's