From Maniples to Cohorts

[Gnaeus Pompeius Magnus]

Upon reading a new book about ancient army formations of the greeks and romans it talks about the manipular legions of the old republic, and the legion of cohorts used by Caesar. I understand the difference between these two different formations, but my question is when and why did they change. Was it just an evolution or metamorhosis caused by the reforms of Marius, or was it something else altogether. I know that the legions of Scipio and the other generals of the 2nd Punic War used Manipular legions, but the book just skips off to Caesar and his Legions of Cohorts without describing the change. Any help would be most appreciated.

[Crispvs]

I have always assumed (possibly incorrectly, but such is the nature of assumptions) that the cohort consisted of three maniples ie six centuries. It has been suggested that the fact that some depictions of signa have a hand at the top and others have a spearhead in the same position may indicate that centuries continued to be organised in manipular fashion into the early empire, with the hand indicating the leading or senior century and the spearhead indicating the rear or junior century.

Crispvs

[Goffredo]

The cohort offered a sizable tactical formation that was denser and had more standing power than simply a bunch of maniples.
It was quite good against Gauls and Germans. The Gauls were proving to be the natural enemy of Rome's future. On the one hand it was obvious that Rome would inevitably expand into Gaul, while the Germans (Cimbri, Teutones) were the immediate cause of the Marius' reforms.

I believe the tactical reforms of Marius were actually quite ripe, resulting as they did from a long manipular tradition that proved many times the worth of the old maniples but also the many defects, were easy to implement with the new levy mechanism that furnished a brand new type of soldier to shape, and urgent with the Cimbri and Teutones romping around so close by!

[Quintius Clavus]

Even during the republic, the allied foot forces were organized as cohorts, not as maniples as the Roman citizen troops were.
It is worth noting that in the late republic, not all cohorts of citizen troops were formally organized into legions. Caesar in his commentaries (Gallic War, Civil War, etc.) mentions bodies of cohorts of citizen troops in some actions along with legions. Eventually most of them did get incorporated into legions, but not necessarily all into one legion.
During the Principate, of course, camp and barracks arrangements still bore the stamp of the maniple - Each cohort with its centuries being paired in the camp rows/barrack blocks. Armies love their "traditions" and the maniple was one of those traditions the Romans continued for a long time - long after it had ceased to have any tactical significance.

Marcus Quintius Clavus/Quinton Johansen

[drsrob]

In my opinion the cohorts consisted of three maniples placed side by side, so a legion arranged with it's cohorts in three lines would have been not that different from the manipular legion, tactically speeking.

[Aryaman2]

There is something I quite don´t understand about the transition from manipular to cohors.
Assuming the cohors is formed by the agregations of themanipuli of hastati, principes and triarii in a single body, the standard Legion deployment being 4 cohors in the front, 3 in second line and the other 3 in the 3rd line, that contrast sharply with the old manipular legion, in which the first line was made up of the 10 manipuli of hastati. What I mean is that a legion with cohors having 8 ranks deep each one would have a total depth of 24 ranks, while the the manipular legion would have just 10-12 ranks in all, counting the 3 lines, so the reformed legion would have a frontage about half the old manipular legion, is that so?

[drsrob]

1. The cohorts might not have been eight ranks deep as the legions still marched 6 abreast in ad 69 (Josephus). A contubernium of 8 men might have included 2 antesignani or light infantryman. That would add up to only 18 ranks
2. The manipular legion would have 2 lines of 6 ranks and one of 3, making 15 ranks.

But this is somewhat beside the point. Many books are not clear about the internal arrangement of the cohort and seam to suggest that the maniples of a cohort were placed behind one another. That would result in not three, but nine lines. In my opinion it's more likely that the three maniples were placed side by side.
The Caesarian legion would then have three lines of maniples/centuries just like the Polybian. That's my point.

[Aryaman2]

6 ranks of Hastati and another 6 of Principes? I thought they were 4 each. Is there any classical source on that?

[drsrob]

6 ranks of Hastati and another 6 of Principes? I thought they were 4 each. Is there any classical source on that?

Not directly.

According to Polybius a maniple of hastati or principes is 120 men strong plus an additional number of velites. the last is not entire clear, but most likely a third of 120 or 40. A contubernium is eight men strong. Most likely the men from a contubernium formed a file.
According to Josephus the Roman army that marched into Palestine under Vespasian marched six abrest. It is generally assumed that each file formed a marching rank.
This all fits in nicely together: a contubernium of 8 composed of a file of 6 plus 2 additional velites

[Crispvs]

Or simply that two of the men of each contubernium have been assigned to other duties, such as accompanying the contubernium's mule or accompanying the pioneers and surveyers at the head of the column.

Crispvs

[drsrob]

Or simply that two of the men of each contubernium have been assigned to other duties, such as accompanying the contubernium's mule or accompanying the pioneers and surveyers at the head of the column.

Crispvs

Another possibility. But I would rather think that the mule would have been accompanied by a slave. And accompanying? The pioneers and surveyors would have been legionnaries themselves, would they not?