Caesar's Double-Strength First Cohorts

[Patrick Waterson]

We tend to assume that the double-strength first cohort was a development of the early Imperial period.  It would seem, however, that Caesar was already using such a formation at Pharsalus.

In Civil War III.89 Caesar "took one cohort from each legion of his third line" to counter Pompey's cavalry manoeuvre.

In Appian's Civil Wars XI.76 he "placed 3000 of his bravest foot-soldiers in ambush"

In Plutarch's Life of Caesar 44 he "ordered six cohorts from the furthermost lines to come round to him unobserved."

In addition, Caesar and Plutarch have Crastinus with a 120-man command: hekaton kai eikosi stratias (a force of 120 men) in Plutarch and electi milites circiter cxx voluntarii eiusdem centuriae (about 120 picked men, volunteers, from his own century) in Caesar.

Putting this all together, we have 3,000 men in six cohorts and a 120-man century in the Tenth Legion which, incidentally, seems not to have been part of Caesar's surprise force.

Caesar's legions were understrength: he had 22,000 men in 80 cohorts, an average of 275 men per cohort, or well below the expected 400-500.  His VIII and IX Legions were combined to form a single legion, so effective average cohort strength was 22,000/70, or c.314 men per cohort - still well short of the 500 we get from combining Plutarch's and Appian's statements.  One is led to conclude that these special-duty cohorts would appear to be double-strength cohorts, one from each legion except the Tenth.

A quick check of the arithmetic supports this: allowing each legion a double-sized first cohort gives 22,000/77 for an average of 285-286 men per normal cohort, and one of 571-572 per first cohort.  Six of the latter amount to 3,248 men, for which Appian's 3,000 is an acceptable representation, given standard rounding conventions.

The Tenth Legion's first cohort was not part of this force: it seems to have had a special job to do, and what this might have been eluded me until Justin Swanton set up the Battle of Pharsalus under his Optio system.  There it could be seen that Pompey's infantry line would have outflanked Caesar's infantry line by 50 yards - so it looks as if the first cohort of the Tenth Legion had the job of covering that extra 50-yard frontage.  Crastinus' volunteer century would probably have had the most exposed spot, the right of the line.  A cohort of c.570 men - say 600 for the Tenth Legion - deployed twelve deep would cover just about 50 yards of frontage.

[Jim Webster]

An interesting thought, when legions start shrinking due to attrition was there any attempt to keep the first cohort up to strength.
If the 1st cohort was recruited from the legion, whilst the other cohorts were filled up by new recruits, then the 1st cohort could stay at close to its proper strength even as the rest of the legion shrank.

Jim

[aligern]

Interestingly that would make it natural to create an expeditionary force from the first cohorts of several legions because they would be he toughest. and best men. That would make a move to 1000 man legions relatively straightforward in the Third century.

I claim no. originality in this.
Roy

[Patrick Waterson]

Thank you, gentlemen: this had not occurred to me.

There may already in the 1st century AD have been a habit of using the (full strength) first cohort as a vexillation: in Tacitus (Annals XV.10) Corbulo, anticipating the need to go to the assistance of a colleague, expediri tamen itineri singula milia ex tribus legionibus et alarios octingentos, parem numerum e cohortibus iussit, that is, ordered 1000 men from each of his three legions with 800 cavalry, and an equal number of infantry from the (auxiliary) cohorts to be in instant readiness.  If there is a little rounding of numbers, he would seem to be taking either two ordinary cohorts from each legion or the first cohort.

[Duncan Head]

We tend to assume that the double-strength first cohort was a development of the early Imperial period.  It would seem, however, that Caesar was already using such a formation at Pharsalus.
...
In addition, Caesar and Plutarch have Crastinus with a 120-man command: hekaton kai eikosi stratias (a force of 120 men) in Plutarch and electi milites circiter cxx voluntarii eiusdem centuriae (about 120 picked men, volunteers, from his own century) in Caesar.

Putting this all together, we have 3,000 men in six cohorts and a 120-man century in the Tenth Legion which, incidentally, seems not to have been part of Caesar's surprise force.

I can't agree with all of that - not the bit about Crastinus and the Tenth, anyway.

Erat C. Crastinus evocatus in exercitu Caesaris, qui superiore anno apud eum primum pilum in legione X duxerat, vir singulari virtute. Hic signo dato, "sequimini me," inquit, "manipulares mei qui fuistis, et vestro imperatori quam constituistis operam date. Unum hoc proelium superest; quo confecto et ille suam dignitatem et nos nostram libertatem recuperabimus." Simul respiciens Caesarem, "faciam," inquit, "hodie, imperator, ut aut vivo mihi aut mortuo gratias agas." Haec cum dixisset, primus ex dextro cornu procucurrit, atque eum electi milites circiter CXX voluntarii eiusdem cohortis sunt prosecuti.

Crastinus was an evocatus, that is roughly a time-expired veteran, who had previously served with the Tenth. That doesn't mean that his 120 voluntarii were on the strength of the Tenth now, although they were deployed next to that legion. And it's milites circiter CXX voluntarii eiusdem cohortis, not centuriae. It looks to me as if Crastinus' unit is a supernumerary force of volunteers, so it can't really be used to say very much about the strength of the legion's established cohorts.

[Patrick Waterson]

I can't agree with all of that - not the bit about Crastinus and the Tenth, anyway.

Crastinus was an evocatus, that is roughly a time-expired veteran, who had previously served with the Tenth. That doesn't mean that his 120 voluntarii were on the strength of the Tenth now, although they were deployed next to that legion. And it's milites circiter CXX voluntarii eiusdem cohortis, not centuriae. It looks to me as if Crastinus' unit is a supernumerary force of volunteers, so it can't really be used to say very much about the strength of the legion's established cohorts.

Definitely 'centuriae' on the Perseus site - here.  Has Renatus du Pontet got it wrong?

Crastinus had been the primus pilus of the Tenth the previous year, so while taking the point about his being an evocatus, I see no reason why he should not be serving with his old legion - Pompey is recorded (Civil War III.88) as having salted two cohorts' worth of 'evocati' among his legions, but Crastinus was of the Tenth and with the Tenth so it seems reasonable to me that he was serving in the Tenth.  And if he was in the Tenth it seems reasonable to assume he was with the first cohort - anything less would hardly be fitting for last year's primus pilus.

[Duncan Head]

"eiusdem cohortis" is from the text at http://www.thelatinlibrary.com/, which doesn't say where its text comes from.  I have no way of knowing which reading is the more likely, but at least drawing 120 men from a cohort need not entail any non-standard unit sizes, so it probably gets the simplicity vote.

Clearly Crastinus wasn't serving as this year's primus pilus himself, yet making last year's primus pilus serve as a lower-ranked centurion, even in the first cohort, would seem an unacceptable demotion. Therefore I still think that his unit must have been supernumerary. (Was it on this forum that we had a discussion about eleven-cohort legions, a year or two ago? Perhaps this is an example, a legion with a supernumerary cohort of evocati and other volunteers attached to its normal ten.)

[Patrick Waterson]

The Penguin translation opts for 'same century', so it looks as if 'centuria' is either the majority manuscript vote or more academically fashionable.  I suspect without being able to prove that the Latin Library text may have suffered a deliberate emendation by someone who was convinced that there could not possibly have been 120 men in a century.

I remember the eleven-cohort legion discussion: your good self pointed out that Luke Ueda-Sarson had spotted a passage in Caesar referring to the recruitment of 22 cohorts in Gallia Narbonensis.  I think the drift of the discussion was about ferentarii and whether the eleventh cohort could consist of same, but assuming these were two legions being recruited, the use of eleven cohorts per legion is interesting.  The organisation is obviously not quite right for a legion with a double-sized first cohort, though the numbers are.

The difficulty with Caesar having anything other than ten-cohort legions at Pharsalus is his own statement that he had 80 cohorts.  Even if we add in the two left guarding the camp (could these be evocati?) we do not get a multiple of 11, and it is difficult to give any of his legions an odd number of cohorts.  One could speculate that he is deliberately omitting supplementary cohorts, though this would raise the question why.

Caesar does note in his account of Pharsalus that Pompey spread his evocati (who had arrived in two cohorts) among his legions.  Caesar makes no mention of himself doing so, which suggests either that his own evocati were deployed as concentrated cohorts (in which case he might at least have eased our peace of mind by terming the men in Crastinus' command 'evocati' rather than 'voluntarii') or were fitted into their old legions, which I believe were not wholly up to strength at the start of the campaign, making reintegration a logical measure.

Agreed that having Crastinus bump the current primus pilus off his perch would be bad form, though we are supposing that Caesar had actually appointed a new primus pilus as opposed to keeping the slot open, putting Crastinus through his official discharge and then welcoming him straight back.  The latter possibility is obviously a conjecture, though one perhaps in keeping with Caesar's demeanour and likely practice.

[Duncan Head]

Even if we add in the two left guarding the camp (could these be evocati?) we do not get a multiple of 11, and it is difficult to give any of his legions an odd number of cohorts.

I wouldn't argue that eleven cohorts was any sort of standard strength; rather, that occasional occurences of ten-cohort legions with a supplementary unit of volunteers attached might have led to some references to cohorts in groups of eleven, and that would be the same thing that I suspect is happening to the Tenth here.

[Patrick Waterson]

Yes, the eleven-cohort legion does seem unusual.  Pompey is noted as having 110 cohorts in 11 legions, which seems to make them cut-and-dried 10-cohort legions, although he also has 7 cohorts (apparently legionary) guarding his camp.  Are these 'eleventh' cohorts drawn from some of the legions or are they part of a legion with three cohorts elsewhere?  At various times both sides spread garrison cohorts around in different locations, though by the time of Pharsalus Caesar seems to have rationalised his arrangements and allocated all of his garrisons from the recently-raised XXVII Legion, allowing him to concentrate his veterans for Pharsalus.  Presumably Pompey had simply assigned a seven-cohort legion from which three cohorts' worth of garrisons had been detached to guard his camp.

If we leave Crastinus in a temporary limbo pending further information, the eleven-cohort recruitment establishment Caesar used in Gallia Narbonensis (strictly speaking this was Lucius not Julius) would make sense in the context of planning a ten-cohort legion with a double-strength first cohort.  This raises a couple of additional questions which may be beyond our present ability to answer.

1) Was it Julius Caesar who invented the double-strength first cohort?  He seems to have had them at Pharsalus, but not in his Gallic campaigns.  Could it have been the result of combat experience, was it a cunning way of getting more troop strength in the same number of legions, was it a combination of the two?  Or was it a way of amalgamating volunteers (perhaps highly experienced evocati) with the legions, either pairing them up with the first cohort or assimilating them into it?

2) Would Caesar have organised the Tenth Legion differently from his other legions at Pharsalus?  Once the VIII and IX have been combined and composited, he has seven effective legions.  When he takes one cohort from each legion for his surprise force, he has six cohorts.  Crastinus and his keen fellows are not in the surprise force (they are engaging Pompey's battle-line and from the manner of Crastinus' demise they are fighting against legionaries), but they are in or directly associated with the X Legion.  Is this because it is differently organised or because the legion has the key right flank position and some or all of the first cohort is needed to cover the extra Pompeian frontage?

I wouldn't argue that eleven cohorts was any sort of standard strength; rather, that occasional occurences of ten-cohort legions with a supplementary unit of volunteers attached might have led to some references to cohorts in groups of eleven, and that would be the same thing that I suspect is happening to the Tenth here.

If Caesar had referred to himself fielding 81 cohorts I would agree.  He does however give himself 80, which suggests he is either rounding the total (something he does not usually seem to do) or one of the other legions is missing a cohort.  Lacking any hint of the latter I am still inclined to think that Crastinus was part of the first cohort and that he was leading a double-strength century.  This does of course raise questions about exactly how Caesar had organised matters regarding his evocati/voluntarii, and lacking conclusive evidence I am happy to agree to differ on this point.

[Duncan Head]

If Caesar had referred to himself fielding 81 cohorts I would agree.  He does however give himself 80, which suggests he is either rounding the total (something he does not usually seem to do) or one of the other legions is missing a cohort.

Or he doesn't regard Crastinus' company as a real cohort, so is happy to claim only 80 cohorts as part of his rhetorical stress on enemy superiority in numbers? This is Caesar, after all, who is neither neutral nor straightforward. We've seen elsewhere how he downplays the presence of his auxiliaries in Gaul, for example, to much the same end.

[aligern]

How does this play out against the cohort counts in Spain? is it possible that the 22 cohorts in the Province are actually just an arbitrRy number of local cohorts, recruited to man defences and without any superior organisation, at least initially?
Somehow the Romans have to get to a sutuation in which there. are cohorts of auxiliaries who are not slingers or archers, but soear, mailshirt and flat shield equipped. Aren't a lot of the Civil War cohorts likely to be these chaps ?
Were the cohorts in the Province citizens?

Roy

[Duncan Head]

It is certainly possible that the 22 cohorts are just an arbitrary collection, yes. I think there may be one or two other references to groups of 11, but I haven't checked lately. 

I don't know if any of the Civil War cohorts are proto-auxilia in equipment terms. Maybe; but we don't seem to have clear reference to any such, while we do hear of cohorts of caetrati so at least some Spanish troops in the Civil War are still armed in traditional local styles. The 22 cohorts of Gaul are non-citizens; but at this stage non-citizens organised into cohorts are often part of a legio vernacula like V Alaudae or Brutus' Macedonian legions (Appian BC 3.79) - in other words, non-citizen status is not yet equivalent to formal differentiation in role or, presumably, equipment.

[Patrick Waterson]

If Caesar had referred to himself fielding 81 cohorts I would agree.  He does however give himself 80, which suggests he is either rounding the total (something he does not usually seem to do) or one of the other legions is missing a cohort.

Or he doesn't regard Crastinus' company as a real cohort, so is happy to claim only 80 cohorts as part of his rhetorical stress on enemy superiority in numbers? This is Caesar, after all, who is neither neutral nor straightforward. We've seen elsewhere how he downplays the presence of his auxiliaries in Gaul, for example, to much the same end.

Either way it looks as if Crastinus was being bracketed with the Tenth and the (sub)unit he was leading was double the strength of a normal century, or at least what Caesar's somewhat attrited legions could be expected to muster as a normal century.

While Caesar is indeed neither neutral nor straightforward, although he liked people to believe he was both, I do not think he would leave out a whole cohort, especially one which performed valiantly and with honour, from his OB.  Thousands or possibly even tens of thousands of auxiliaries maybe, but not the creme de la creme of his troops and his most dedicated supporters.

Looking again at the text, Crastinus says to his men: "Sequimini me, manipulares mei qui fuistis ..."  (Follow me, you who were my fellow-soldiers/comrades ...) which suggests that the men concerned are of the first cohort of the Tenth Legion, he having until recently been primus pilus.  The question is whether they were (i.e. used to be) his fellow soldiers (manipulares) because they had left, because he had left, or both.  As he was an evocatus I incline to the second option, although it does not entirely exclude the third.

[Jim Webster]

I wonder if in the civil war, as people were doing things on the fly and no one was quite sure who was in charge where at times, whether in some places cohorts were raised and then brought together to form legions, rather than just legions being raised.

Jim