 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.