Like Americans, the Romans thought of themselves as a nation of immigrants. The story of Rome's founding begins with Aeneas, a refugee from the burning city of Troy, who wanders the Mediterranean for years with his people searching for a new home, as told most poignantly in books two and three of Vergil's Aeneid. Romulus and Remus, Aeneas's descendants, actually founded the city of Rome as a new settlement and invited others to join them. Despite these origin stories, the Romans could be ambivalent or even outright hostile to migrants. Yet they also did extend citizenship rights to non-Romans, that is, one did not have to be born a Roman; one could become a Roman, which comparatively speaking was a rather expansive view. Most ancient societies that had a concept of citizenship had a very strict understanding of who was a citizen. The Athenians, for all their reputed openness, typically did not permit non-citizens to become citizens; they allowed non-citizens to live with them, but these non-citizens, metics as they called them, were a separate class. The Romans, by contrast, had mechanisms for extending citizenship and citizen rights to non-Romans. This is not to say standards were always consistently applied or worked to the advantage of non-Romans. From time to time, the Romans expelled groups of people they found dangerous, including philosophers (161–154 BCE), Jews (139 BCE), Chaldeans (139 BCE), and worshippers of Bacchus (186 BCE). The Romans could be undeniably brutal to conquered peoples, frequently killing and enslaving those they defeated in battle, but the Romans recognized that over time there were benefits to moving these defeated peoples from subjects to be governed to participants in the Roman political community.

As could be expected, the Romans gave citizenship, or a limited version of it, first to those who lived closest to them. Over time, the sense of who belonged to the Roman political community spread until in 212 CE the emperor Caracalla granted citizenship to all free peoples living within the boundaries of the Roman Empire. However, as mentioned above, there were occasional complications to the process, and the Romans of the first century BCE faced the greatest citizenship crisis Rome ever had. For decades, Rome's Italian allies had been clamoring for some form of citizenship.