The Roman Republic spent its first two and a half centuries (or so) expanding fitfully through peninsular Italy (that is, Italy south of the Po River Valley, not including Sicily). This isn’t the place for a full discussion of the slow process of expanding Roman control (which wouldn’t be entirely completed until 272 with the surrender of Tarentum). The consensus position on the process is that it was one in which Rome exploited local rivalries to champion one side or the other making an ally of the one by intervening and the other by defeating and subjecting them (this view underlies the excellent M.P. Fronda, Between Rome and Carthage: Southern Italy During the Second Punic War (2010); E.T. Salmon, The Making of Roman Italy (1982) remains a valuable introduction to the topic). More recently, N. Terranato, The Early Roman Expansion into Italy (2019) has argued for something more based on horizontal elite networks and diplomacy, though this remains decidedly a minority opinion (I myself am rather closer to the consensus position, though Terranato has a point about the role of elite negotiation in the process).

The simple (and perhaps now increasingly dated) way I explain this to my students is that Rome follows the Goku Model of Imperialism: I beat you, therefore we are now friends. Defeated communities in Italy (the system is different outside of Italy) are made to join Rome’s alliance network as socii (“allies”), do not have tribute imposed on them, but must supply their soldiers to fight with Rome when Rome is at war, which is always.

It actually doesn’t matter for us how this expansion was accomplished; rather we’re interested in the sort of order the Romans set up when they did expand. The basic blueprint for how Rome interacted with the Italians may have emerged as early as 493 with the Foedus Cassianum, a peace treaty which ended a war between Rome and [the] Latin League (an alliance of ethnically Latin cities in Latium). To simplify quite a lot, the Roman “deal” with the communities of Italy which one by one came under Roman power went as follows:

• All subject communities in Italy became socii (“allies”). This was true if Rome actually intervened to help you as your ally, or if Rome intervened against you and conquered your community.
• The socii retained substantial internal autonomy (they kept their own laws, religions, language and customs), but could have no foreign policy except their alliance with Rome.
• Whenever Rome went to war, the socii were required to send soldiers to assist Rome’s armies; the number of socii in Rome’s armies ranged from around half to perhaps as much as two thirds at some points (though the socii outnumbered the Romans in Italy about 3-to-1 in 225, so the Romans made more strenuous manpower demands on themselves than their allies).
• Rome didn’t impose tribute on the socii, though the socii bore the cost of raising and paying their detachments of troops in war (except for food, which the Romans paid for, Plb. 6.39.14).
• Rome goes to war every year.
• No, seriously. Every. Year. From 509 to 31BC, the only exception was 241-235. That’s it. Six years of peace in 478 years of republic. The socii do not seem to have minded very much; they seem to have generally been as bellicose as the Romans and anyway …
• The spoils of Roman victory were split between Rome and the socii. Consequently, as one scholar memorably put it, the Roman alliance was akin to, “a criminal operation which compensates its victims by enrolling them in the gang and inviting them to share to proceeds of future robberies” (T. Cornell, The Beginnings of Rome (1995)).
• The alliance system included a ladder of potential relationships with Rome which the Romans might offer to loyal allies.

Now this isn’t a place for a long discussion of the Roman alliance system in Italy (that place is in the book I am writing), so I want us to focus more narrowly on the bolded points here and how they add up to significant changes in who counted as “Roman” over time. But I should note here that while I am calling this a Roman “alliance system” (because the Romans call these fellows socii, allies) this was by no means an equal arrangement: Rome declared the wars, commanded the armies and set the quotas for military service. The “allies” were thus allies in name only, but in practice subjects; nevertheless the Roman insistence on calling them allies and retaining the polite fiction that they were junior partners rather than subject communities, by doing things like sharing the loot and glory of victory, was a major contributor to Roman success (as we’ll see).

First, the Roman alliance system was split into what were essentially tiers of status. At the top were Roman citizens optimo iure (“full rights”, literally “with the best right”) often referred to on a community basis as civitas cum suffragio (“citizenship with the vote”). These were folks with the full benefits of Roman citizenship and the innermost core of the Roman polity, who could vote and (in theory, though for people of modest means, only in theory) run for office. Next were citizens non optimo iure, often referred to as having civitas sine suffragio (“citizenship without the vote”); they had all of the rights of Roman citizens except for political participation in Rome. This was almost always because they lived in communities well outside the city of Rome with their own local government (where they could vote); we’ll talk about how you get those communities in a second. That said, citizens without the vote still had the right to hold property in Roman territory and conduct business with the full protection of a Roman citizen (ius commercii) and the right to contract legal marriages with Roman citizens (ius conubii). They could do everything except for vote or run for offices in Rome itself.

Next down on the list were socii (allies) of Latin status (note this is a legal status and is entirely disconnected from Latin ethnicity; by the end of this post, Rome is going to be block-granting Latin status to Gauls in Cisalpine Gaul, for instance). Allies of Latin status got the benefits of the ius commercii, as well as the ability to move from one community with Latin status to another without losing their status. Unlike the citizens without the vote, they didn’t automatically get the right to contract legal marriages with Roman citizens, but in some cases the Romans granted that right to either individuals or entire communities (scholars differ on exactly how frequently those with Latin status would have conubium with Roman citizens; the traditional view is that this was a standard perk of Latin status, but see Roselaar, op. cit.). That said, the advantages of this status were considerable – particularly the ability to conduct business under Roman law rather than what the Romans called the “ius gentium” (“law of peoples”) which governed relations with foreigners (peregrini in Roman legal terms) and were less favorable (although free foreigners in Rome had somewhat better protections, on the whole, than free foreigners – like metics – in a Greek polis).

Finally, you had the socii who lacked these bells and whistles. That said, because their communities were allies of Rome in Italy (this system is not exported overseas), they were immune to tribute, Roman magistrates couldn’t make war on them and Roman armies would protect them in war – so they were still better off than a community that was purely of peregrini (or a community within one of Rome’s provinces; Italy was not a province, to be clear).

The key to this system is that socii who stayed loyal to Rome and dutifully supplied troops could be “upgraded” for their service, though in at least some cases, we know that socii opted not to accept Roman citizenship but instead chose to keep their status as their own community (the famous example of this were the allied soldiers of Praenesti, who refused Roman citizenship in 211, Liv. 23.20.2). Consequently, whole communities might inch closer to becoming Romans as a consequence of long service as Rome’s “allies” (most of whom, we must stress, were at one point or another, Rome’s Italian enemies who had been defeated and incorporated into Rome’s Italian alliance system).

But I mentioned spoils and everyone loves loot. When Rome beat you, in the moment after you lost, but before the Goku Model of Imperialism kicked in and you became friends, the Romans took your stuff. This might mean they very literally sacked your town and carried off objects of value, but it also – and for us more importantly – meant that the Romans seized land. That land would be added to the ager Romanus (the body of land in Italy held by Rome directly rather than belonging to one of Rome’s allies). But of course that land might be very far away from Rome which posed a problem – Rome was, after all, effectively a city-state; the whole point of having the socii-system is that Rome lacked both the means and the desire to directly govern far away communities. But the Romans didn’t want this land to stay vacant – they need the land to be full of farmers liable for conscription into Rome’s armies (there was a minimum property requirement for military service because you needed to be able to buy your own weapons so they had to be freeholding farmers, not enslaved workers). By the by, you can actually understand most of Rome’s decisions inside Italy if you just assume that the main objective of Roman aristocrats is to get bigger armies so they can win bigger battles and so burnish their political credentials back in Rome – that, and not general altruism (of which the Romans had fairly little), was the reason for Rome’s relatively generous alliance system.

The solution was for Rome to essentially plant little Mini-Me versions of itself on that newly taken land. This had some major advantages: first, it put farmers on that land who would be liable for conscription (typically placing them in carefully measured farming plots through a process known as centuriation), either as socii or as Roman citizens (typically without the vote). Second, it planted a loyal community in recently conquered territory which could act as a position of Roman control; notably, no Latin colony of this sort rebelled against Rome during the Second Punic War when Hannibal tried to get as many of the socii to cast off the Romans as he could.

What is important for what we are doing here is to note that the socii seem to have been permitted to contribute to the initial groups settling in these colonies and that these colonies were much more tightly tied to Rome, often having conubium – that right of intermarriage again – with Roman citizens. The consequence of this is that, by the late third century (when Rome is going to fight Carthage) the ager Romanus – the territory of Rome itself – comprises a big chunk of central Italy […] but the people who lived there as Roman citizens (with and without the vote) were not simply descendants of that initial Roman citizen body, but also a mix of people descended from communities of socii throughout Italy.

Bret Devereaux, “Collections: The Queen’s Latin or Who Were the Romans, Part II: Citizens and Allies”, A Collection of Unmitigated Pedantry, 2021-06-25.