This book is not primarily a political history of Rome in which a factual reconstruction and an account of struggles for power, and among powers, form the very fabric of the narrative; nor is it a social and economic history. I ammainly concerned with the collective norms and regulations that went into building Rome’s institutional architecture. The Continental – especially German and Italian – tradition of legal historiography abounds in studies on Roman public law or Staatsrecht, starting with Mommsen’s masterpiece, whose influence can still be felt in all of our work. If I have ventured to add yet another volume to an already copious literature, however, it is because of my growing dissatisfaction with much of this scholarship. The formalism typical of our disciplines, including the history of the law, has very deep roots, and has lent the tradition the weight of scientific authority. A large number of important works have come out of this tradition that seek to describe and analyze in detail the countless component parts of the complex machine that was Roman law. Such works, however, seem less interested in examining how this machine functioned concretely. In short, they are unable – to use a well-known image by a great nineteenth-century Roman historian, Rudolf von Jhering – to move beyond a system’s anatomy to the study of its physiology. In my experience of modern legal historiography, I have encountered impressive reconstructions that have had a lasting impact on the field, but which basically propose models that could not have worked in practice, making them of little use for an understanding of the way in which such a society operated.