branches of large families. New cognomina were coined and came into fashion throughout Roman history. Under the Empire, the number of cognomina increased dramatically. Where once only the most noble patrician houses used multiple surnames, Romans of all backgrounds and social standing might bear several cognomina. By the third century, this had become the norm amongst freeborn Roman citizens. The question of how to classify different cognomina led the grammarians of the fourth and fifth centuries to designate some of them as agnomina. For most of the Republic, the usual manner of distinguishing individuals was through the binomial form of praenomen and nomen. But as the praenomen lost its value as a distinguishing name, and gradually faded into obscurity, its former role was assumed by the versatile cognomen, and the typical manner of identifying individuals came to be by nomen and cognomen; essentially one form of binomial nomenclature was replaced by another, over the course of several centuries. The very lack of regularity that allowed the cognomen to be used as either a personal or a hereditary surname became its strength in imperial times; as a hereditary surname, a cognomen could be used to identify an individual's connection with other noble families, either by descent, or later by association. Individual cognomina could also be used to distinguish between members of the same family; even as siblings came to share the same praenomen, they bore different cognomina, some from the paternal line, and others from their maternal ancestors. Although the nomen was a required element of Roman nomenclature down to the end of the western empire, its usefulness as a distinguishing name declined throughout imperial times, as an increasingly large portion of the population bore nomina such as Flavius or Aurelius, which had been granted en masse to newly enfranchised citizens. As a result, by the third century the cognomen became the most important element of the Roman name, and frequently the only one that was useful for distinguishing between individuals. In the later empire, the proliferation of cognomina was such that the full nomenclature of most individuals was not recorded, and in many cases the only names surviving in extant records are cognomina. By the sixth century, traditional Roman cognomina were frequently prefixed by a series of names with Christian religious significance. As Roman institutions vanished, and the distinction between nomen and cognomen ceased to have any practical importance, the