"Understrength units and frontage" Topic

In the horse and musket era, which is one with which I'm more familiar, it was common practice for troops holding ground to try to occupy a particular width. As the unit became attenuated by losses, whether on a battlefield or between battles through campaign attrition, they would typically still try to defend the same given frontage. If necessary they would do so by thinning the formation, so that a three-deep line that had lost a third of its strength might go to a two-deep line in order to maintain the same frontage. The intervals between formations in the battle line would thereby remain the same, gaps would not start to open out, and so on.

This is a very general summation and I don't want to bring an anachronistic discussion of Napoleonic formation depth to the Ancients boards. Generally the musket-era preference for maintaining constant width was because when you went from 3-deep to 2-deep, you gave up very little firepower if any, and it was by firepower that you won your fights. Therefore you maintained frontage over depth because this kept your formation effective in the way that counted most.

What I do want to understand is whether the same was true in say 100AD. If a Roman cohort nominally 480 men strong were reduced by campaign attrition to 360 men, would it form for battle

- still 8 men deep but only 45 wide?
- still 60 wide but only 6 deep?
- something else again?

i.e. was it about width or was it about depth?

My assumption initially was that they'd maintain the depth at the expense of frontage. But if so, and if fighting in a line of cohorts alongside each other, to do so would shorten the cohort's front, which would allow gaps to develop in exactly the same way as in later wars – which could compromise the integrity of the whole front.

Cohorts weren't standalone units and presumably whatever was done was done in co-ordination with the rest of the formation. Does any contemporary writer discuss how understrength units adapted? Do we think the solution adopted by a cohort that started the battle understrength would be different to the one it would adopt if it lost that number during the battle? Were cohorts genuinely organic tactical formations, or were they administrative formations that were rebalanced for the battlefield into equalish units? I.e. would a 360-man and a 480-man cohort adjust themselves to a pair of 420-man cohorts? Would two cohorts at 50% strength merge to make one good one? Would the First Cohort distribute its additional men to weakened junior cohorts to address this?

Thoughts and especially contemporary cites most welcome.

Matching frontage was as important in ancient warfare as in any other period. Greek Hoplite formations were known to thin the ranks in order to match the frontage of their opponents. It is quite probable that practice carried over to Roman warfare as well. At Pharsalus it is thought that Caesar thinned the ranks of his understrength cohorts in order to match the frontage of Pompey. Given that each cohort has its' own chain of command it is difficult seeing them merged but anything is possible and I am as curious as you are if there is evidence that this was done.

From my readings it appears a cohort was recruited and stayed as a unit throughout its career. I too doubt they would break up or merge cohorts.

Was it the Thebans who beat the Spartans by deepening their phalanx at the expense of it's width?

From my readings it appears a cohort was recruited and stayed as a unit throughout its career. I too doubt they would break up or merge cohorts.

I think this is extremely questionable, and I have never seen any primary source evidence indicating this. Under the Republic, legions would be raised for as long as necessary, but rarely that many years at a stretch, save for the 2nd Punic, and so would be demobilised together. Same goes for the warlords of the late Republic demobilising excess legions, eg Augustus after Actium.

The idea, however, that the Principate legions never added recruits to keep established cohorts up to strength seems to me quite fanciful. When you are requiring your soldiers to serve at over two decades before they are eligible to retire, given the likely attrition from disease, let alone combat, the chances of you having a meaningful force after even ten to fifteen seem a tad on the low side. It also means that you would lose an entire cohort of veteran soldiers in one go, and have to recruit and train a whole new cohort to replace them.

In modern times, the only military that I can think has taken that route was the Soviets post WW2, and there they were simply interested in a conscript sausage factory whereby they had roughly one battalion within a regiment at any one time that was actually fully trained. More professional armies have always sought to leaven even large numbers of recruits with older, more experienced soldiers, eg the US Army's cadre system when raising even whole new divisions during WW2, where existing formations were forced to transfer some of their manpower to be the foundation of the new formation.

In short, I just do not buy it.

Would it not also depend on training? A Century was trained within a cohort so it would possibly find it less efficient to be outside its parent formation. The Romans established the conternubia as a group of 8 mess mates which would increase comradeship so my guess would be the units would stay together for cohesiveness but adjust frontage where necessary. Purely a guess….

Was it also the Romans that had the cohorts based on experience so the battle line would have a mix? They were arranged in battle so that the strongest and weakest units would be mixed throughout the formation, Cohort I was made up of the elite troops, Cohorts II, IV, VII, and IX consisted of the weaker, and often newest, soldiers. It was not uncommon to find raw recruits in these Cohorts. Cohorts III and V had no specific designation. Cohort VI, Cohort VIII and Cohort X were the best after the 1st.

These arranged as four cohorts in the first line, and three in the next two. SO with 6 good cohorts and 4 raw or new, it was easy to have a line of four good in the front, then 1 good and 2 raw in the next two lines.

Of course, this is all conjecture.

The background to the question is that I am contributing painting to the Waterloo in 1/72 at 1:1 scale project that is going on. In the course of doing this, I've appreciated the sight of full-size battalions rather than 12- or 20-figure tabletop "equivalents". It has occurred to me that at some point, I might paint a 1:1 early Imperial cohort. This would take about a year of spare time. I might then add more cohorts, of plausibly unequal sizes, at which point it becomes important to understand how reduced strength affects frontage.

I'm also interested in supposed formations. One frequently sees a chessboard array with cohort-wide gaps between cohorts and a supporting line of more cohorts behind, offset so that if they advanced they'd fill the gaps. This seems highly implausible because your whole front line is then 50% gaps into which the enemy can attack, so he overwhelms you at odds of 2:1 well before your second line can come up. Is there any evidence for such a formation? Why wouldn't you form up in two continuous rows of five?

I think only wargamers dash into every gap which opens in the enemy line. Real. Life is a bit more complex and scary.

Phil Sabin discusses unit frontages, depths and intervals fairly convincingly in "Lost Battles".

This seems highly implausible because your whole front line is then 50% gaps into which the enemy can attack, so he overwhelms you at odds of 2:1 well before your second line can come up. Is there any evidence for such a formation?

The evidence is that is what the contemporary writers say happened during the Middle Republic period. Of course, another matter entirely whether they did so during, say, the early principate. But as Martin says, it might be damned foolish for an enemy to rush into such gaps. If the second line is only a hundred yards back, the attacker who is supposedly being so clever flanking the front line elements gets flanked in turn. Not to mention the minor issue of having to try to wheel in any form of formation into the supposed exposed flank. It is the very real risk of basing conjecture on little MDF stands of toy soldiers rather than real flesh and blood on a scary battlefield.

DBS303 – Perhaps I should have been more clear. I was referring to the Principate, not the Republic. When you raise a legion every year then that's not a problem.

Going from memory I recall that the IXth lost three, (I think), cohorts during the Boudican revolt. I recall that they were described as new recruits.

During one of the Numidian wars, (again I think), the IXth which seems to have been a hard luck unit, had a cohort isolated at a fortlet. They were outside the fortlet when attacked. The cohort, again noted as recruits, broke and ran leaving their centurion alone to cover the retreat alone. He died and the cohort was decimated as punishment.

"Not to mention the minor issue of having to try to wheel in any form of formation into the supposed exposed flank."

A barbarian army wouldn't wheel as a unit. They'd just 'mob' into the exposed flank.

"Is there any evidence for such a formation?"

For what it's worth I'd say that Hannibal's first attack at Zama would count. When the Romans left lanes in their formation so the elephants would pass through would count. If all the second line just did a left face and march forward they'd be directly behind the first line. I've read theories that the checkerboard only lasted until shortly before contact, then the second line marched forward to fill in the gaps.

The point is that, regardless of whether one wheels smartly, or just mobs into the flank, the second line will then hit you in your flank about twenty or thirty seconds later if they are at all competent. And that assumes that someone in the front rank of the attacking unit thinks it a good idea to turn into the "exposed" flank in the first place, and can then lead/persuade his fellows to follow him.

I would also note that for writers in the early principate, defeat by barbarians was something that needed explaining and excusing, so I would be a little cautious about accepting descriptions of "new recruits" at face value. Perhaps they were units with a significant proportion of more recent recruits, but that does not mean there was not equally perhaps some sort of veteran cadre. At the time of the Boudiccan revolt, it is quite possible that the lads of the IXth had not seen serious military action for several years, and had been employed more on engineering and general garrison duties, being in the eastern "rear area" of the province.

Caesar describes the legions as being in 'quincunx' formation, i.e., arranged as the dots on a die showing '5'.

The troops are in three rows, with the units in the middle row stationed behind the gaps in the first row.