However, the cognomina eventually became family names, and so agnomina were needed to distinguish between similarly-named persons.
Pseudo-Probus uses the hero of the Punic Wars, Publius Cornelius Scipio Africanus, as an example: Men's personal names are of four types, praenomen, nomen, cognomen and agnomen: praenomen for instance Publius, nomen Cornelius, cognomen Scipio and agnomen Africanus.Marius Victorinus further elucidates: Now the agnomen comes from outside, and in three styles, from personality or physique or achievements: From personality, such as Superbus ["Haughty"] and Pius [displaying the Roman syndrome of virtues including honesty, reverence to the gods, devotion to family and state, etc.
True Roman nicknames, fully replacing the individual's name in usage, are rare.
Caligula's agnomen came from the little boots that he wore as part of his miniature soldier's uniform while accompanying his father, Germanicus, on campaigns in northern Germania.
In turn, Germanicus received his agnomen in 9 BC, when it was posthumously awarded to his father Nero Claudius Drusus in honour of his Germanic victories.