Drusus

Drusus was a cognomen in Ancient Rome originating with the Livii. Under the Republic, it was the intellectual property and diagnostic of the Livii Drusi. Under the empire and owing to the influence of an empress, Livia Drusilla, the name was used for a branch of the Claudii into which she had married: the Claudii Drusi. During that period, when a line reached two or three branches calling for four or five names, the Romans shortened to one or two; consequently, "Drusus" could seem to be used in place of a praenomen. True praenomina, however, could be assigned to anyone within the customary usage of their clan, but Drusus could only be used in lines that had it as an agnomen.