Roman Naming Conventions

[Nathan Ross]

How did one differentiate between Roman brothers in a family who had the same nomen?

It depends on the era.

Originally the praenomen was used to distinguish between brothers (eg Marcus Antonius Creticus had three sons - Marcus Antonius, Gaius Antonius and Lucius Antonius; Marcus Licinius Crassus had two sons, Marcus Licinius Crassus and Publius Licinius Crassus, etc)

From the late republic and early empire onwards, brothers tended more often to have different cognomens (eg Lucius Caecilius Cilo had two sons, Lucius Caecilius Valens and Publius Caecilius Secundus). Sometimes different cognomens were drawn from the mother's family as well, to stress dynastic connections, or from patrons or friends.

By the later second and early third centuries, the praenomen had largely fallen out of use, and so many people were adopting imperial nomens that the cognomen became the only name that most people used!