Organization of Roman legion in the Maniple and Cohort structures

Testudo formation demonstrated by reenactors. Photo courtesy of Adobe Stock.

Best description of the maniple and cohort structure for a Roman legion that I’ve read can be found in Roman Soldier Operations Manual: Daily Life * Fighting Tactics * Weapons * Equipment * Kit by Simon Forty.

This post will sketch out what the organization looks like in both structures.

The building block units of a legion will be shown, with the number of soldiers in each unit illustrated.



Book says the maniple structure was used from the 4th century B.C. until about 107 to 101 B.C. at the time of the Marian reforms.

There were three lines in a maniple. The front line of least experienced troops were the hastati.  Middle line were the principe. Back row was the older and most experienced soldiers, the triari.

The basic building block was the contuberium, or squad, which consisted of 6 soldiers who shared a tent and cooked their meals together.

A contuberium would look like this, with the soldier count listed and total for the unit:

1 1 1
1 1 1
6 total


A principe and hastati formation would have 60 soldiers, in 10 contuberia of 6 men each. A formation, consisting of squads and total head count would look list this:

6 6 6 6 6
6 6 6 6 6
60  total


A triarii formation would look like this:

6 6 6 6 6
30  total


A centuriae, or century of soldiers, would like like this:

triarii, back 30
principe 60
hastati, front 60
total 150


Two centuriae would make up a maniple:

triarii, back 30 30
principe 60 60
hastati, front 60 60
total 300


A legion would consist of 20 maniples.  (Quite a few specific comments in the book say the legion had 20 maniples.) The maniple was the main operating unit, each of which could operate independently if needed.

So a legion, with its 20 maniples would look like this:

300 300 300 300 300
300 300 300 300 300
300 300 300 300 300
300 300 300 300 300
6000  total


Alternative structure of Maniple

A line of unarmored skirmishers would be in front of the hastati. They had darts or light spears used to harass an enemy. When the armored opponents drew near, the skirmishers would withdrawn through the line and the hastati would move forward.

A few paragraphs after providing the above description of 20 maniples of 300 soldiers each, the book says the typical structure of a maniple legion would be:

  • 4,500 heavy infantry
  • 1,000 volites, or skirmishers
  • 300 cavalry
  • 200 other
  • 6,000 total

The book does not explain the different structures, 6,000 heavy infantry in 300 man maniples versus 4,500 heavy infantry plus 1,000 volites plus 300 cavalry. Ten squadrons of cavalry had 30 horsemen each.

I don’t have any idea how to reconcile the two different descriptions.

I redrew my outline assuming 15 maniples of 300 soldiers instead of 20 maniples as follows:

10×30 mbr cavalry sqdn 300
other/rounding/artillery 200
infantry maniple 300 300 300 300 300
infantry maniple 300 300 300 300 300
infantry maniple 300 300 300 300 300
skirmishers/60/maniple 1000
total 6000


Image courtesy of Adobe Stock.



The Marian reforms restructured the army in many ways, including transitioning from a 6,000 man legion to a 5,500 man legion. Those changes also got rid of the triarii, principes, hastati, and velite distinctions.

I’ve also read in several sources that a legion had 4,500 men in the cohort structure. Don’t have any idea how to reconcile the 4,500 versus 5,000 count.

Keep in mind those are authorized strengths. Actual strength would in all likelihood have been far less.

The book provides a more detailed picture of the staffing of a cohort.

A contumerium, or squad, had 8 soldiers led by a decanus:

1 1 1 1
1 1 1 1


A century, or company, consisted of 10 contuberniae of 8 men each.  The command element consisted of a centurion and an optio, his second in command. A century looked like this, including the command element:

8 8 8 8 8
8 8 8 8 8

Format of these charts lists the command element, the building block units, with a total man count at the bottom.


A cohort consisted of 6 centuriae, or companies.  The command element, or principales included: a signifer, tesserarius, and cornicen. The cohort was structured as:

82 82 82
82 82 82
495 total


The 1st cohort was about double strength at 800 men, consisting of five double strength companies. It contained the most experienced legionaries. Its structure:

162 162 162 162 162
813 total


A legion had 9 cohorts at about 480 line soldiers plus the 1st cohort at about 800.

There would be a cavalry unit of 120 horsemen.

The command element consisted of the Legate, 6 tribunes, Praefectus Castrorum, and the Aqulifer.

In addition there would be about 103 more, to round out the legion at a theoretical size of 5,500.

A few pages later, the book says a legion would have 10 catapults, one for each cohort. Several other long distance weapons would be on hand.  I’ll assume the 103 other soldiers would be the ballistarius, or artillerymen.

This would create the following picture of a fully staffed legion in the cohort structure:

9 command
120 cav.
103 art.
813 495 495 495 495
495 495 495 495 495
5500 total


The total strength of a cohort legion would be approximately:

  • 5,268 – heavy infantry legionnaires in cohort, including commanders
  • 120 – cavalry, including commanders
  • 103 – ballistarius, or artillerymen
  • 9 – command element
  • 5,500 – total legionnaires


What do you think of this description? Is it useful? Did I miss something? Goof my math?

2 thoughts on “Organization of Roman legion in the Maniple and Cohort structures

  1. In dealing with antiquities, it is often difficult to grasp what was common, everyday usage for them & which (in their minds) didn’t require further explanation for future historians. Good info.

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