I ought to give you some background on Roman names, because this is a subject that is often misunderstood.
The Classical System
This naming system, which only applied to full Roman citizens, is often called the tria nomina system, which suggests three names. In truth, Romans could have anything from two to six names, depending on when they are examined.
We often call Romans by names that reflect the ‘wrong’ parts of what they called themselves. Julius Caesar did not have a personal name Julius and a family name Caesar. His full name was Gaius Julius Caesar, or rather Iulius, since Rome had no letter J (or W, while U and W sounds were represented by V).
The middle of those three names, Iulius, was his clan name (nomen (plural nomina) or nomen gentilicium); the clan (gens, plural gentes) was a marker of status and honour. The family claimed descent from the mythical Aeneas, whose son was often called Iullus. Famous individuals could give their personal names to clans by adding the letter I to their names so Marcus, whoever he was, started the Marcius clan. Names could be altered to sound more Roman; the Sabine family Clusus were such public benefactors than they were given citizenship and their name changed to Claudius (Appius Claudius paid for the Appian Way road that you can still walk along today, as well as Rome’s main aqueduct the Aqua Appia). Tiberius, Caligula, Claudius and Nero all carried that nomen.
Prestige could run both ways. One of the Claudius clan aspired to the position of Tribune, only open to plebeians, and had himself adopted by a plebeian man called Clodius who was young enough to be his son, and changed his name and status.
Many of the Romans you will encounter in history books were related to each other, so you will find in full names many with the nomen Cornelius. Because of the excessive similarity of names, historians and classicists have tended to use other parts of the figure’s name for clarity. Because so many had the same name and were only distantly related, people started to subdivide the clan names.
The ‘Caesar’ in Gaius Julius Caesar relates to that subdivision, so his immediate group were termed Iulii Caesares.
Often the name related to a well-known characteristic of the founder of the sub-clan. ‘Caesar’ relates to caesura, meaning ‘cut’. (He was not born by caesarean section by the way. The procedure did not exist at the time, and anyway it does not explain why his father, uncles and the rest already had the name.) The politician Sulla was Lucius Cornelius Sulla, where Sulla means ‘stain’; it is believed that he may have been an albino with the red skin marks sometimes associated with the condition. Cicero was Marcus Tullius Cicero; Cicero means ‘chickpea’; either one of his ancestors had a mark on his nose like one or the family were once greengrocers; Shakespeare calls him ‘Tully’, and also calls Virgil ‘Marro’, a reminder that we have today constructed names that were not always used in the past.
This final name was called the cognomen, from Latin cognosco, ‘I know’.
In addition, males bore a personal name, the praenomen, ‘pre-name’. There were only eighteen of them, of which a dozen were in regular use. Many of them are numbers (Tertius, Quintus, Sextus, Septimus, Octavius, Decimus), while Spurius originally meant ‘illegitimate’, Postumus ‘posthumous’, Publius ‘of the people’. There were very few names and all of them had a standard abbreviation (Lucius – L., Titus – T., Gaius –C. (sic), and so on. It was not possible to create a new name. When a praenomen was not known, it was assumed to be Gaius. The main use of praenomina was in inheritance, military service, legal writs, electioneering and similar activities.
When adopted, the adopted son took the adoptive father’s name and modified his former nomen. So Gaius Octavius upon adoption in the will of his great-uncle Gaius Julius Caesar took the name Gaius Julius Caesar Octavianus.
So far, I have talked about male names. They may seem odd to you, but female names were even odder. While women in the early days of Rome had possessed personal names (the wife of Romulus was called Hersilia), they vanished over time (but were never formally abolished). The daughter of Marcus Tullius Cicero was just called Tullia. So she received her father’s nomen and sometimes cognomen, but had no praenomen and thus no personal name. This sounds to us like sexism, but was not so. If her father’s nomen was Cornelius, she would be called Cornelia. Julius Caesar’s aunt was called Julia. The nomen alone would tell everyone she was a woman from a high-born family. She might also use the sub-clan cognomen, so Publius Clodius Pulcher had a sister Clodia Puchra (pulcher means ‘good-looking’, a good reason to keep it). So a female didn’t need a personal name; her nomen was enough to protect her throughout life. If she acquired sisters, they might be known as Prima, Secunda and Tertia and so on, but these were informal and were usually dropped. Two women of the same gens but a different generation in the same household might result in one taking a diminutive form, such as Livia and Livilla (‘little Livia’). But that was rare. Roman women did not change their name on marriage. In fact, unless they married according to Manus, a rare form of marriage which prohibited divorce, they actually remained within their father’s family for life, and husbands had to write them into their wills.
It may seem odd not to have a personal name, but think of this: the only females they knew who had a personal name were foreigners, non-citizen subject women (peregrinae) and slaves. By denying themselves a personal name, they acquired status. Once married, they would be the only one in the household with their name, as their sons and daughters took their husband’s name. In the later empire, this changed, especially for Christians, and Greeks within the empire had a typical Greek name structure. Constantine’s mother was called ‘Flavia Julia Helena’.
When adopted, males took their adopted father’s name in full, dropped their own praenomen, and modified their nomen. So when Gaius Julius Caesar adopted (in his will) his great-nephew Gaius Octavius (a name so lowly that he had no cognomen), the boy became Gaius Julius Caesar Octavianus. So that’s four. He’s known for a while (and in Antony and Cleopatra) as Octavian, but was later given the title/name Augustus, the lucky one. No wonder Cicero said to him ‘Boy, you have nothing to commend you but your name’.
Emperors often have ridiculously long names. Caracalla was born Lucius Septimius Bassianus, then became Marcus Aurelius Septimius Bassianus Antoninus, ending up as Caesar Marcus Aurelius Severus Antoninus Pius Augustus; happily posterity calls him by a nickname: a caracalla was a type of Gaulish cloak.
This name inflation applied not only to emperors: the fifth century Gallo-Roman poet we call Sidonius Apollinaris was actually Gaius Sollius Modestus Apollinaris Sidonius. (His wife Papianilla and daughters Roscia and Severina had their own names).
Freed slaves (liberti) took the name of their former master, now their patron, to which their own slave name was appended. Similarly, those raised to full citizenship on an imperial grant might pick the emperor’s name as part of the family name. Gnaeus Julius Agricola may have had an ancestor who received citizenship from Julius Caesar, who founded Forum Iulii (now Fréjus); despite being descended from Gaulish nobility, his name is fully Roman (Agricola means ‘farmer’ in Latin).
When used in inscriptions, the full name would typically include a filiation, usually that of the father (indicated by ‘f’ – filius (son) or ‘filia’ (daughter) followed by that parental name in the genitive case). From the late Republic onwards the full name might also include the voting tribe, a marker of status. Honorific names or other distinguishing names might be added in a man’s (rarely a woman’s) lifetime: the military hero Quintus Fabius Maximus had Verrucosus (‘warty’) added and later Cunctator (‘delayer’) owing to his tactics against Hannibal).
The mass registration of new citizens under the law of Caracalla in AD212 caused the system of first names to collapse, since all males were automatically called ‘Marcus Aurelius’. A new system arose which included ‘Aurelius’ as a signifier of citizenship, a non-Roman given name and a patronymic. This included the fourth century African Roman historian Aurelius Victor. Latterly a locative name was used (e.g. Victor of Vita, Procopius of Gaza, Helena of Constantinople).
Christianisation brought into use saints’ names (Maria, Anna, Johannes) and Greek names associated with Christianity (Eudoxia, wife of Theodosius II, was born Athenais, but renamed to hide the pagan name).
Like much towards the end of the Roman world, we find a tight system had collapsed, something which the quasi-barbarian inheritors took advantage of, stressing their Roman or barbarian roots as they wished in order to claim particular ancestry.
By the sixth century parents in Gaul and elsewhere chose a Latinate name for a son destined for the Church and a Germanic one intended for royal service. We hear of people with Germanic names also having Latin names, and of people entering Frankish royal service changing their names to become more Germanic.