This essay makes the case that Livy's version of the tale of Mettius Fufetius transmits certain facts that relate to inherited ritual practices (horse-sacrifice among them) along with formulas used in early law and diplomacy. Although the author may not be fully aware of the original meaning of all he is handing down (e.g., the etymology of mitis ) because he has simply taken materials from his sources without much critical investigation, the traditional elements are important to him because they seem to authenticate this legend about the reign of Tullus Hostilius. For the moralizing historian that Livy certainly is, the treason of Mettius Fufetius and his execution at the command of the Roman king comprise the starting point of a remarkable sequence of episodes in his narrative that demonstrate the dishonorable behavior of Rome's chief rivals in Italy. The legend of Mettius Fufetius thus embodies a kind of ““original sin”” in the political realm, and becomes the paradigm for Rome's harsh dealing with faithless allies over the next five centuries. The essay concludes that this story typifies many Roman fabulae , insofar as they were often composed on the basis of outdated or unfamiliar idionyms, toponyms, ceremonial words and phrases, and ancient legal terms. In such fabulae characters like Tullus Hostilius and Mettius Fufetius, perhaps mere names in annals and king-lists, become the performers whose ceremonial acts turn into the foundational moments of Rome's public life.