The earliest indicator we have of what is going to be Rome’s socii-system is the Foedus Cassianum (“Cassius’ Treaty”) concluded with the communities of Latium – the Latins – in 493. That is, of course, quite an early date and while we have narratives of these events from both Livy and Dionysius of Halicarnassus, we have to be quite cautious as they are operating at great chronological remove (both writing in the first century B.C.) and with limited sources (something both actually more or less admit). According to Livy (2.18) the issue had begun with thirty Latin towns conspiring in a league against Rome (which does not yet have any imperial holdings), to which Rome responded by going to war. The timing, just a few years after the expulsion of Rome’s kings and the formation of the res publica may be suggestive that the Latins had formed this league to take advantage of the political crisis in Rome, which was the largest town in Latium, in order to throw off whatever Roman influence they may have been under during the period of the kings.

In any case, the Romans win the war and impose a peace treaty the terms of which, according to Dionysius of Halicarnassus went thusly:¹

Let there be peace between the Romans and all the Latin cities as long as the heavens and the earth shall remain where they are. Let them neither make war upon another themselves nor bring in foreign enemies nor grant a safe passage to those who shall make war upon either. Let them assist one another, when warred upon, with all their forces, and let each have an equal share of the spoils and booty taken in their common wars. Let suits relating to private contracts be determined within ten days, and in the nation where the contract was made. And let it not be permitted to add anything to, or take anything away from these treaties except by the consent both of the Romans and of all the Latins.

This is the origin point for Rome’s use of what I’ve termed the “Goku Model of Imperialism” – “I beat you, therefore we are friends”. Having soundly defeated – at least according to our sources – the Latins, Rome doesn’t annex or destroy them, nor does it impose tribute, but rather imposes a treaty of alliance on them (in practice I suspect we might want to understand that Rome’s position was not so dominant as our sources suggest, thus the relatively good terms the Latins get). The treaty sounds like an equal relationship, until one remembers that it is the entire Latin league – thirty or more communities – as one party and then just Rome as the other party.

I will still make no apologies for this visual gag.
Image modified by Bret Devereaux.

Rome proceeds, in the century or so that follows, to use this alliance to defeat their other neighbors, both the nearest major Etruscan centers as well as the Aequi and Sabines who lived in the hills to the north-east of Rome and the Volsci who lived to the south of Latium. Roman relations with the Latins seem to fray in the early 300s, presumably because the greatest threat to their communities was increasingly not the Volsci, but Rome’s emerging regional power. That leads to a collapse of the Foedus Cassianum in 341 and another war between Rome and the Latin League. Once again our sources are much later, so we might be somewhat skeptical of the details they provide, but the upshot is that at the end the Romans won by 338.

Rome’s expansion into most areas follows a familiar pattern: Rome enters a region by concluding an alliance with some weaker power in a region and then rushing to the aid of that weaker power; in some cases this was a long-term relationship that had been around for some time (like the long Roman friendship with Etruscan Caere) and in some cases it was a very new and opportunistic friendship (as with Capua’s appeal to the Romans for aid in 343). In either case, Rome formed a treaty with the community it was “protecting” and then moved against its local enemies. Once defeated, it imposed treaties on them, too. Rome might also seize land in these wars from the defeated party (before it imposed that treaty); if these were far away, Rome might settle a colony on that land rather than annexing it into Rome’s core territory (the ager Romanus). These new communities – the Latin colonies – were created with treaty obligations towards Rome.

Note the change: what was initially an alliance between one party (Rome) and another party (the Latin League) has instead become an alliance system, a series of bilateral treaties between Rome and a slew of smaller communities. And they were smaller, because Rome often took land in these wars, so that by the third century, the Roman citizen body represented roughly 40% of the total, making Rome much bigger than any other allied community. This shift was probably gradual, rather than there being some dramatic policy change at any point. Rome accrued its Italian empire the same way it would accrue its Mediterranean one: as a result of a series of localized, ad hoc decisions which collectively added up to the result without ever being intended to constitute a single, unified policy.

The Romans called all of these allied communities and their people socii, “allies” – a bit of a euphemism, because these were no longer equal alliances. We’ll get into the terms in a moment, but it seems clear that by 338 that these “allies” are promising to have no foreign policy save for their alliance with Rome and to contribute soldiers to Roman armies. So Rome is in the driver’s seat determining where the alliance will go; Rome does not have to consult the allies when it goes to war and indeed does not do so. The socii cannot take Rome to war (but Rome will go to war immediately if a community of socii is attacked). This is no longer an equal arrangement, but it is useful for the Romans to pretend it is.

The next major series of Roman conflicts are with the Samnites. Rome is, according to Livy, at least, drawn into fighting the Samnites because of its suddenly concluded alliance with Capua and the Campanians (though Rome had been more loosely allied to the Samnites shortly before). In practice, the first two Samnite Wars (343-341, 326-304) were fought to determine control over Campania and the Bay of Naples, with Rome fighting to expand its influence there (by making those communities allies or protecting those who were) while the Samnites pushed back.

The Third Samnite War (298-290) becomes something rather different: a containment war. Rome’s growing power – through its “alliance” system – was clearly on a course to dominate the peninsula, so a large coalition of opponents, essentially every meaningful Italian power not already in Rome’s alliance system, banded together in a coalition to try to stop it (except for the Greeks). What started as another war between Rome and the Samnites soon pulled in the remaining independent Etruscan powers and then even a Gallic tribe (the Senones) in an effort to contain Rome. The Romans manage to pull out a victory (though it was a close run thing) and in the process managed to pull yet more communities into the growing alliance system. It seems – the sources here are confused – that the decade that followed, the Romans lock down much of Etruria as well.

The Greek cities in southern Italy now at last recognize their peril and call in Pyrrhus of Epirus to try to beat back Rome, leading to the Pyrrhic War (280-275). Pyrrhus wins some initial battles but – famously – at such cost that he is unable to win the war. Pyrrhus withdraws in 275 and Rome is then able over the next few years to mop up the Greek cities in Southern Italy, with the ringleader, Tarentum, falling to Rome in 272. Rome imposed treaties on them, too, pulling them into the alliance system. Thus, by 264 Rome’s alliance system covered essentially the whole of Italy South of the Po River. It had emerged as an ad hoc system and admittedly our sources don’t give us a good sense of how and when the terms of the alliance change; in many cases it seems our sources, writing much later, may not know. They have the foedus Cassianum, with its rather more equal terms, and knowledge of the system as it seems to have existed in the late third century and the dates and wars by which this or that community was voluntarily or forcibly integrated, but not the details of by what terms and so on.

Bret Devereaux, “Collections: How to Roman Republic 101, Addenda: The Socii“, A Collection of Unmitigated Pedantry, 2023-10-20.

---

1. trans. Earnest Clay (1940).