Roman Nomenclature
A.   Male Citizens

Roman citizens (male) had a complex system of names, which distinguished them from all other peoples of the ancient world, who mostly used a personal name with a patronymic. All Romans had two names (1 and 2 below) and most three as well: these are the three names (tria nomina) by which those who were (or tried t pass themselves off as) Roman citizens can be distinguished in the absence of any other evidence.

1.      The praenomen (“ fore-name”)
The personal or “first” name: these were chosen from a very short list available for boys (Roman unimaginativeness appears in the use of “fifth”. “sixth”, “seventh” and “tenth” as names). Since these are normally abbreviated in inscriptions, Latin texts, and modern histories, a key is provided:

A.     Aulus  M.   Marcus  Sex. Sextus
Ap.  Appius  M’   Manius Ser. Servius
C.   Gaius Mam.  Mamercus      Sp. Spurius
Cn.  Gnaeus   P.   Publius T. Titus
D.   Decimus Q.  Quintus Ti. Tiberius
L.  Lucius          S.  Septimius    

2.      The nomen (“name”)
Also called gentilicum (“clan name”). The main “family” or ancestral name: the most common of these derived from old aristocratic families or clans, but had spread very widely to their dependents and freed slaves, and to provincials on whom members of such families had conferred citizenship. Because they were so widespread, the third name was needed to distinguish different branches, even within the Republican aristocracy. A rare or unusual gentilicum is commonly evidence of descent from some Italian community, rather than from Rome or the provinces. Here are the commonest (and most aristocratic) gentilica

   i.       of imperial families: Aelius, Aurelius, Claudius, Flavius, Iulius, Ulpius

  ii.      of some old families of the Republic: Aemilius, Antonius, Caecilius, Calpurnius, Cornelius, Domitius, Fabius, Iunius, Licinius, Pompeius, Sulpicius, Valerius.

3.      The cognomen
The additional “family” name, used to distinguish branches within the same “clan” in the aristocracy. Among those who received Roman citizenship, it was common practice to retain as cognomen their original, non-Roman name and to pass it on to their descendants. Two groups should be noted:
   i.      free-born foreigners (peregrini): on becoming citizens they adopted the gentilicum of the Roman governor from whom they received the citizenship (under the Republic) or of the reigning Emperor (from Augustus onwards), and often his praenomen as well, but kept their native name as cognomen.

  ii.      Slaves set free by Romans (“freedmen”, “liberti”) themselves normally became Roman citizens: they would take the praenomen and gentilicum of their former owner (“patron”), and keep their old personal name as cognomen: freedmen who belonged to a woman take her father’s praenomen and gentilicum.

n.b. Some cognomina are patently non-Latin and reveal that the person was himself a form of foreigner or slave or a descendant of one: but such people could also, instead of transliterating their old names, adopt a Latin translation, which does not reveal their origin so clearly.
Hence, some examples:
C(aius) Iulius Caesar: Roman aristocrat
L(ucius) Annaeus Seneca: provincial citizen of Italian municipal descent
M. Ulpis Adcobrovati f. Novantico: enfranchised provincial (CIL. 16 160)

M. Ulpius Aug. lib. Hermias: imperial freedman (ILS. 1593)

4.      Additional elements:
a)      Agnomina (“added names”)
There was nothing to prevent an individual taking or being given a fourth, fifth or even more names: in some cases they would die with him, but in others they would be transmitted to his descendants. Among the sources of agnomina are :
i)                    nicknames, not always complimentary, e.g. Naso (big-nose), Flaccus (flap-ears)
ii)                   names to record a general’s victories: e.g. P. Cornelius Scipio Africanus (“conqueror in Africa”),  Nero Claudius Drusus Germanicus (“conqueror of Germany”); from Augustus such names became the exclusive preserve of the imperial family, and emperors adopted them in increasing numbers.
iii)                 Names signifying an adoption from one family to another, a common practice in the aristocracy to prevent families dying out. The adopted person would take the tria nomina of his adoptive father but add the gentilicum of his natural father with the letters “-an-“ inserted, to show his origins: e.g. C. Octavius, when adopted by C. Iulius Caesar, became C. Iulius Caesar Octavianus. The same end could be served by taking one’s original cognomen, or even both nomen and cognomen, as additional names: indeed under the Empire it became the fashion for senators to accumulate strings of names, and the consul of A.D. 169 boasted of no less than 38.
b)      Filiation
Between the nomen and cognomen was often inserted a record of the father’s and even the grandfather’s name in the following abbreviated form: the initial letter of the father’s praenomen followed by f. (for “filius”, son) and of the grandfather’s followed by n. (for “nepos”, grandson); e.g. C. Iulius C. f. C. n.  – C.(aii) f.(ilius), son of Gaius; C.(aii) n.(epos), grandson of Gaius. This was no doubt done to distinguish between cousins with the same praenomina.
In the case of freedmen, whose natural fathers were slaves, the filiation was replaced by a reference to the patron in the form of the patron’s praenomen followed by “L.” or “lib” ( = freedman): e.g. T. lib., Titi libertus, “freedman of Titus”.  Slaves freed by a woman, whatever her name,  are “Gaiae liberti” (C. lib).

c)      Voting tribe
In the full form, this filiation was in turn followed by the initial letters of one of the hereditary voting units in which all plebeian citizens were enrolled: see list of the 35 tribes with abbreviations.
An example of a full name: P. Cornelius P.f. Scipio Africanus (“conqueror of Africa”) Aemilianus (an Aemilius adopted by a Cornelius Scipio): no tribe, because he was a patrician.

B.   Roman Women
They simply took the feminine form (ending in –a, not –us) of their father’s gentilicia or cognomina, or of both. In time additional elements from other ancestors came to be added. E.g. Iulia, Aemilia Lepida. A filiation might also be added. L.f  L(uci) f(ilia).
C.   Foreigners (peregrini)

As indicated above, these most commonly called themselves X, son of Y; outside their own communities they might add “Athenian”, “Arvernian”, etc. These names could be turned into latin, where the names often looked rather odd, e.g. Diomedes, Artemonis f., Phrygius ( a Phrygian), Tutius, Buti f., Dacus (a Dacian) (both soldiers in the Roman auxilia, ILS. 1988, CIL. 16.13)