Cohort commander?

[Nathan Ross]

You are both using different numbers. But where do you get them from? what are our sources? Do we have a surviving firsthand account of about it?

No we don't, really, which is partly the point. There are a couple of military treatises from the Roman era, but they aren't exactly free from confusion and neither do they necessarily complement each other. Hyginus' 1st century work on laying out a camp gives some figures for unit sizes (8 men in a tent group, 480 in a cohort, double-size first cohort etc), while Vegetius, writing in (probably) the late fourth century gives some alternative figures - 555 men in a standard cohort, but only 5 centurions! (he implies that the centuria was obsolete by his day).

The multitude of surviving career inscriptions for centurions and other officers, meanwhile, provides us with a lot of detail about military rank and hierarchy (demonstrating, apparently, that the six traditional centurion positions from the republic survived into the six-century imperial cohort, for example). Unfortunately, interpreting this mass of evidence is often very difficult, as titles and terms altered over the years and were perhaps rather mutable anyway.

The more you study the Roman army, I often think, the more you come to realise that most confident assertions of military structure and numbers - including a lot of what you read in popular history books - is based on conjecture and best-guesswork.

On the matter of the cohort commander (or not), I'd still recommend the Ross Cowan article I mentioned in my first post ('The Centuria in Battle' - Ancient Warfare Special issue 2010), and particularly the section called 'The Cohort Command Conundrum'.

While granting that several historians believe that the cohort was commanded by the pilus prior (he specifically mentions Brian Campbell, War and Society in Imperial Rome, 2002), Cowan maintains that there was no such commander in practice - the cohort functioned as 'a grouping of cooperative centuries'. His view is supported to some extent by the lack of any reference in literature or inscription to a dedicated cohort commander, or to a cohort standard before the 4th century (when Vegetius provides it with a draco). Absence of evidence, of course, is not evidence of absence, but it's curious that such a pivotal figure, if he existed, goes completely unmentioned!

Cowan is drawing heavily (it seems) on B.H. Isaac's 'Hierarchy and Command Structure in the Roman Army', in the same author's The Near East Under Roman Rule (1998). Isaac explains the 'absence of middle tactical management' in the legion as a product of communication limitations on the battlefield. The individual centurion 'led as many soldiers as could be effectively commanded by a single man in the chaos of battle' (Cowan, p.48), and no senior figure was possible or required.

The desire to establish a cohort commander, whether the pilus prior or one of the tribunes, comes, Cowan suggests, from a misapplication of modern military principles to ancient armies.

For a study of careers within the centurionate, detailing what can be established of the complexity of hierarchy and command, I suggest Robert Summerly's thesis Studies in the Legionary Centurionate (1990), which I believe is available online somewhere!

For a comparison of the legionary centurion and the officers of the equestrian tres militiae (including some possible reasons why centurion or prefect level officers might not have commanded citizen cohorts) see Brian Dobson's 'Legionary Centurion or Equestrian Officer, a comparison of pay and prospects' in Ancient Society 3 (1972). Alternatively, Yann le Bohec's The Roman Imperial Army provides a fairly detailed summary of command hierarchy based on available evidence.

Hope that helps a bit - like I say, there's seldom one single interpretation of anything to do with the Roman army (or indeed history in general!), so it pays to remain open minded. But that doesn't mean, of course, that you can just believe whatever you like...