First off we need to establish what changes are generally understood to fall under the heading of the “Marian Reforms”, before we then try to actually locate those changes in our evidence (and then marvel at our general inability to do so). Understood broadly the Marian reforms are supposed to be a combination tactical, organizational and equipment reforms associated with Gaius Marius in the last decade of the 100s. As it turns out, Marius initiated almost none of these reforms, some of these supposed reforms didn’t happen at all at any point and some of them happened outside the time period in question.

In short, the things that are supposed to have happened here are:

• (Tactical-Organizational) A shift in battle tactics from the two-century maniple (c. 120 men) to the six-century cohort (c. 480 men) as the primary tactical unit on the battlefield,¹ as well as the primary organizational unit of the Roman army. Elements of the older Polybian legion persist in names and titles.
• (Organizational) A shift from poorly paid conscript soldiers drawn from Rome’s propertied class (the assidui) drawn up through the dilectus to the use of volunteers drawn from Rome’s property-less poor (the proletarii or capite censi) who served as effectively professional soldiers, lacking any other means of subsistence.
• (Organizational) The practice of granting land and/or citizenship to Roman soldiers on discharge as a regular feature of Roman service.
• (Organizational) The end of the light infantry velites and Roman citizen cavalry (the equites) as part of the legion, as a product of the next point making such wealth distinctions unimportant.
• (Logistical) The introduction of state-supplied equipment (in place of self-supplied equipment) which enabled the mass-recruitment of the proletarii, as they no longer needed to be able to afford their own equipment, as part of a reform ascribed by some scholars to Gaius Gracchus (trib. 123-2).
• (Equipment) The introduction of a new design of pilum with a wooden rivet designed to break on impact with enemy shields (Plut. Mar. 25).
• (Equipment) The prioritization of the aquila, the eagle standard, over other standards in the legion (Plin. NH 10.16), often framed as the aquila fully replacing these other standards.
• (Equipment) The introduction of the furca, a Y-shaped pole for carrying the soldier’s pack (the sarcina), leading to better legionary logistics.

As we’re going to discuss, some of these things happened – but not because of Marius – and some of them didn’t happen at all. So how on earth did this idea of a big “Marian Reform” end up so pervasive in how we (used to) understand the Roman army of this period? The answer really has a lot to do with gaps (lacunae) in our sources. For the early second century, we have two really quite good sources on Roman military activity, Livy and Polybius. But both give out by mid-century,² leaving us relatively blind until Julius Caesar‘s comentarii (de Bello Gallico and de Bello Civili) suddenly give us a massive infusion of information as we can see Caesar’s army functioning often in quite minute detail.

And we see what seem to be quite different armies! Caesar is using cohorts as tactical and operational units, rather than maniples. His armies don’t seem to have any citizen cavalry in them and they seem to be very loyal to him; he’s using a lot of non-citizens in auxiliary roles in a way that we know will become very standard in the imperial period (eventually making up half the army by Tiberius‘ reign). And indeed, moving forward, the legions of the early empire end up a lot more visible to us, both because of the literary evidence (Tacitus!) and also because, as they become more stationary on fixed frontiers, they leave forts and inscriptions and other evidence we can see far more clearly than the ever-moving armies of the Roman Republic.

And then into that there is Gaius Marius. Remember that our sources in this period are a bit patchier, without a strong continuous narrative (but with a lot of sources so we generally have someone for most of it). But Marius gets a lot of focus because of his roles in the civil wars and his spectacular seven consulships, and the one thing we are told quite clearly about him is that in 107 when he raised his first consular army he broke tradition by accepting volunteers from the proletarii (Sall. Iug. 86.1; Plut. Mar. 9.1). The temptation then to see that substantial change (which, to be clear, our sources are exaggerating for reasons I’ll discuss in a moment) as connected to all the other changes from the “Polybian” legion to the “Caesarian” legion and thus to assume that Marius is doing all of them, reading far too deeply into a few lines of Sallust and Plutarch (the latter not generally a particularly good guide on military affairs).

And I should note finally at the outset that this all also plays into a tendency in our sources generally: ancient authors really like narratives where one particular aristocrat can be credited with making major reforms or innovations as an expression of their particular virtue. We’ve talked about this with Lycurgus, but it shows up consistently with rulers supposedly introducing new weapons and new practices as big, top-down reforms that, on closer inspection, turn out to be gradual changes we can see signs of happening over quite some time. It’s an understandable if irritating bias of habit for authors whose purpose in writing is the education of aristocrats on how to be leaders – every big change has to be a product of the character and leadership of aristocrats (even when it wasn’t). Plutarch, especially, of all ancient authors, loves these sorts of just-so stories and guess who we are heavily reliant on for the life of Gaius Marius? But until relatively recently, historians were often far more willing to accept these sorts of just-so stories than they should have been (in part because late 19th and early 20th century historians shared some of those same assumptions about elite leadership and in part because singular reforms make for compelling stories).

Bret Devereaux, “Collections: The Marian Reforms Weren’t a Thing”, A Collection of Unmitigated Pedantry, 2023-06-30.

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1. Note that the size of the century has changed, from 60 to 80 as well.

2. Polybius’ history, already incomplete as we have it, ends, while Livy’s continuous narrative which originally went through the first century cuts out almost completely in 167, leaving us with just summaries of his work.