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.
Vipsania Marcella Vipsania Marcella Vipsania Marcella Agrippina or Marcellina or Vipsania Tertia (born 27 BC or later) was perhaps the only daughter of Roman statesman Marcus Vipsanius Agrippa by his second wife Claudia Marcella Major. If so, she was the first grandchild to Octavia Minor and first great-niece to Roman Emperor Augustus. If she truly had the name Marcella, there is no way that she was a daughter of Agrippa's first wife, Caecilia Attica. She and her elder sister Vipsania Agrippina were married off to Quintus Haterius (cos. 5 BC), Publius Quinctilius Varus (cos. 13 BC) and Tiberius (also cos. 13 BC)