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.
Agrippina the Elder was made "princeps". While Germanicus was administering the oath of fealty to Tiberius, a mutiny began among the forces on the Rhine. During the mutiny, Agrippina brought out their sixth child, Gaius, and made preparations to take him away to a safer town nearby. He was in a full army outfit including the legionary hobnailed boots ("caligae"). These military-booties earned Gaius the nickname "Caligula" (lit. "little boots"), and garnered sympathy for Agrippina and the child among the soldiery. Tacitus attributes her actions as having quelled the mutiny (Tacitus, "Annals" 1.40–4). Once the mutiny was put to an end, Germanicus allowed