Many had a third name, the cognomen (additional name, nickname;
often denoted a branch of a family).
The cognomen originally showed a peculiarity personal to one
individual, e.g., Scaevola ("Lefty"), Balbus ("Lisper"), Cursor ("Runner",
perhaps "Speedy"). An inherited cognomen, however, did not indicate
a personal characteristic other than descent from the original holder of
the name.
A second cognomen (or agnomen) could be added to show
an achievement: P. Cornelius Scipio Africanus (conqueror of Africa).
A person adopted into another gens could also be identified
by an adjectival name indicating his family of birth:
P. Cornelius Scipio Aemilianus, the son of L. Aemilius Paullus; Scipio
Aemilianus was born an Aemilius.
Some families were so large (and so often favored the same praenomen)
that most men in the family soon acquired nicknames in order to be distinguished
from each other, for example, the Metelli, many of whom [or at least many
of those encountered in a history textbook] were named Q. Caecilius Metellus.
But they are easy to tell apart when called by their last two names:
Metellus Numidicus = Q. Caecilius Metellus Numidicus (fought successfully
in Numidia) and his son
Metellus Pius = Q. Caecilius Metellus Pius (so-called for his devotion
to his father's rights)
There were few individual first names in common use; these were abbreviated on inscriptions and in documents. When pronouncing these names, it is proper to say the whole name, not the initial.
A. Aulus
Ap. (App.) Appius
C. Gaius
Cn. Gnaeus
D. Decimus
K. Kaeso
L. Lucius
M. Marcus
M'. Manius
Mam. Mamercus
N. Numerius
P. Publius
Q. Quintus
Sex. Sextus
Ser. Servius
Sp. Spurius
T. Titus
Ti(b). Tiberius