Leviticus 18:14

Who....affinity. Hebrew, "she is thy aunt." Some say that, in the old law, a person might marry his niece, but not his aunt; as the order of nature would be inverted if the aunt were subject to her nephew. But others assert that the law was reciprocal, and excluded the marriage of both. The emperor Claudius married his niece Agrippina, and authorized others to do the like. But only one imitated him at Rome; (Suetonius) though Tacitus (An. xii.) says, other nations did it with solemnity, as they had no law to the contrary. Aliis gentibus solemnia, &c. (Calmet)