Proving that you were a Roman citizen was actually quite important in Ancient Rome. Whether or not you were a citizen determined your rights and this could even mean your right to be free. Slavery today is considered immoral but in the Ancient World, slavery was the norm rather than the exception. In the early 1st century AD only about five million of the over fifty million inhabitants of the Roman Empire were free and full Roman citizens 1.
wearing toga (20–30 AD)
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Cives Romani: The cives romani were full Roman citizens. They were subdivided into two classes: the non optimo iure, who had rights of property and marriage and the optimo iure, who also had the right to vote and hold office.
Latini: The Latins were a tribe living in Latium in central Italy who came under Roman control at the close of the Latin War (340–338 BC) noting that the term Latini came to include people of non-Latin background. The Latini held a number of rights similar to those of Roman citizens (the Latin Rights or ius Latii in Latin) but they did not have the right of marriage (ius connubii).
Socii : The Socii or Foederati were citizens of states which had treaty obligations with Rome and had certain rights in exchange for agreed levels of military service.
Following the Social War (91–88 BC), the Lex Julia was passed in 90 BC giving full Roman citizenship to all Latini and Italian socii states (and the socii states that had not participated in the Social War) and the Latini and socii levels of citizenship disappeared.
Provinciales and freedmen: The provinciales were people from the provinces who were under Roman control or influence, but who only had basic rights under international law (ius gentium). Freedmen were former slaves who had gained their freedom and were not automatically given Roman citizenship. Their children however were born free citizens.
When in doubt, anyone could just ask around about a person's social standing and reputation. This made even more sense in a society where those who could read and write were the exception rather than the norm. In a small town, word of mouth was often the only way people had to prove their Roman citizenship.
Language and clothing also played a role in determining if a person was a Roman citizen or not. An individual who spoke good Latin, who behaved and dressed in certain ways, displayed his status and Roman identity. Only Romans could wear the toga and it was strictly forbidden for non-citizens, foreigners, freedmen and slaves to wear it in Roman territories. Men of infamous career (e.g. actors) or shameful reputation were also forbidden to wear the toga.
In 24 AD it became a criminal offense to adopt the three-part name (tria nomina) if an individual was not a citizen and using the tria nomina by non-citizens was considered a type of forgery. Provincials usually used one or two names (their name and the name of their fathers) and it was very common for people in the provinces to have only one name. Slaves usually only had one name, either the name they had before enslavement or the name assigned to them by their master. Upon receiving his freedom and Roman citizenship, a male slave took the praenomen and nomen of his master and kept as cognomen the name he had been called as a slave or changed it to a Latin or more Latin sounding name1.
The census data was collected from member lists that were kept by the various tribes. The censors called each tribe separately and took the names of the members of each tribe according to these tribal lists. The paterfamilias then had to appear in person before the censors who were seated in curule chairs and had to declare under oath ("declare from the heart") the names of the members of his family and all his property (e.g. location and description of the land, number of slaves). These official lists formed the Tabulae Censoriae which were deposited in the aerarium or the temple of Saturn (in earlier times in the Atrium Libertatis and in later times in the temple of the Nymphs).
If a person's Roman citizenship was in doubt or proof of citizenship was needed for a transaction, an inquiry could easily be made to verify the name on the list from the last census. Witnesses, usually individuals from the tribe, would also have to confirm that you are the person in question, bearing always in mind that pictures were not available back then. Once in a while, a freedman (libertus) or even a foreigner posing as a togate citizen was ferreted out in the census. The punishment for falsely claiming Roman citizenship was very severe. According to Suetonius it was death by having your head removed with an axe. The Romans took citizenship very seriously!
If a child lived in the provinces, his father or some duly appointed agent, made a declaration (professio) before the provincial governor at the public record office (tabularium publicum). In the course of his professio the father or the agent declared that the child was a Roman citizen. The professio was entered in the register of declarations (album professionum) 3. The father or the agent then received a wooden diptych which was the certified private copy of the professio and which contained the names of seven witnesses.
a Boian soldier of the Ala
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A freed slave would take the praenomen and nomen of his master and keep the cognomen which was the name he was called as a slave unless he decided to change it to a more Latin sounding name 1. The enfranchisement of freedmen was recorded in a documentary tabella manumissionis 4. Therefore freedmen also had documentary evidence of their status.
To prove their Roman citizenship abroad, Romans could produce the grant of citizenship or their birth certificate, which both were in the form of the previously mentioned diptych which was small enough for citizens to carry when they were out of town 1. If they were doubts regarding the person claiming to be a citizen or the document itself, witnesses could be called5.
However it was not always easy to find witnesses far away in the provinces. For example, in 70 BC Verres, the corrupt governor of Sicily, questioned Gavius' citizenship claim. Gavius, a Roman citizen of Compsa, had protested about Verres' treatment of Roman citizens. According to Cicero, Gavius cried out that he was a Roman citizen and that he had served in the Roman army under the Roman knight Lucius Raecius who was in Panhormus (today's Palermo) at the time. Gavius was executed nevertheless by means of crucifixion (a type of execution forbidden for Roman citizens)6.
Verres ultimately had to face the consequences of his actions and was tried. This goes to show that what mattered most in the Roman world was a citizen's social network rather his legal status. A citizen's social network could impose consequences and provincial governors / foreign authorities had to beware of the consequences before mistreating any Roman citizen, especially an upper class Roman citizen. More than the documentary evidence, what mattered the most was the citizen's connections.
Documentation also made it more difficult for a slave to escape. A runaway slave would usually have to run quite far and... quite fast, away from his town and his master. As soon as he ran away, advertisements with a precise description of him would be posted in public places and rewards offered. Professional slave-catchers would also be hired to catch him and anybody found harboring a slave would be punished. Additionally, the slave would have to find food and shelter and ... a job. However, if he was able to reach a new town or even a city like Rome, people would at some point question his identity, at least once every five years during the census. At that point, the slave would need to provide documentary evidence of his status and failure to do so meant that his true identity could be revealed. And slaves could not easily fake a document as most of them could not read or write. Thus, if caught (and if not executed) escaped slaves would be branded on the forehead with the letters "FUG" for fugitivus. Nevertheless, some slaves managed to escape to far away provinces but the perils along the way were great!
Incredible facts about Roman citizenship