By Paul Blake Volunteer Guide

The Roman Auxiliary Cohort - Command and Control in the 3rd and 4th centuries

During my tours as a Vindolanda guide, I often get questions about military history of the site and the relationship between different ranks in the Roman army. For example, how do a Centurion and a Prefect compare to each other? And can we equate Roman ranks and grades with contemporary examples? In this three-part blog I will explore the chain of command of an Auxiliary Cohort at Vindolanda and how control was exercised.

Probably the most interesting, but also the most confusing of structures of command and control at Vindolanda can be found at junior level. While there is a clear and defined role of the prefect and the centurions, little is recorded as to the subordinate officers. As in all historical records much is made of emperors, commanders, leaders and officers but little is recorded as to the role of subordinates.

Subordinate command within each century would have comprised soldiers of two grades - the principales, and the immunes. The former in modern terms easily equate to Senior NCOs (SNCOs) in executive or command roles. The latter are however a little more difficult to clarify as the group is made up from the administrators, technicians and tradesmen of the cohort. By the 3rd century the main difference was pay. Soldiers received basic pay, immunes pay and a half and the principales double pay.

In each century there were four subordinate officers to the centurion. The most senior was the signifer (standard bearer), who additionally carried out all the pay and paperwork for the century. Below him was the optio who took command in the absence of the centurion. The reason the latter takes command over his senior being both are modern warrant officers, but the signifier is the century’s administrator whilst the optio is the century’s executive soldier - its ‘Company Sgt Major’. These two soldiers are principales and receive double pay.

The signifier would probably have previously served as an optio and aspiring for selection or commissioning to centurion.. The optio in his own right could be selected by either the prefect or his centurion for detached duties.

The other two SNCOs are the tesserarius (roughly the provost Sgt) and the custus armorum (quartermaster Sgt) responsible for weapons and equipment. These two ranks attract the pay and a half of immunes but are both of higher status.

On campaign, the cohort probably fought as one body in line of centuries, the prefect mounted, taking overall direction from the rear with the standard of the cohort. In the front rank of each century would be the centurion, the signifer; both in full regalia and the optio, carrying his staff of office at the rear ‘persuading’ the rank and file to fill gaps and maintain the line. No better example of that is the Queen's birthday parade at Horse Guards where the red jacketed guardsmen form line of companies, their captain and flag bearer to the fore and the company sgt major, pace stick in hand monitoring standards from behind the rear rank. Some things do not change.

Again, in the field the cohort would have, if at full strength paraded a prefect, six centurions and 6 centuries of 80 men. However, in barracks those sub-units would have been massively reduced as soldiers were subordinated to other tasks within the fort. These included extra mural activities, detachments, external guard duties and tasking within the fort away from their centuries. As the Vindolanda strength return tablets show, in an earlier century this system would reduce considerably the number of troops available at Vindolanda at any one time - two thousand years later that is exactly the same with the average 650 infantry battalion probably having half that number when in barracks.

In auxiliary units the cohort had to provide and sustains for itself in all aspects. The immunes provided the staff for specialist duties. Initially without either additional rank or pay they received immunity from guard duty and heavy fatigues (in barracks) and importantly were outside the influence (in barracks) of their centurion. Hadrian introduced pay and a half later but there is no evidence of higher grade of rank. In this group, the list is endless but includes the clerks, storemen, hospital orderlies, wood and stone masons et al. Current excavations (2021) may even indicate the presence of master bakers.

The mystery is: how were all these activities controlled, co-ordinated and supervised? In the principia (HQ) the home of the centurions would have command enough. The rank and file provided the guards and heavy labour but who was in control? Did the optio’s have specific responsibilities - stores, workshops, messing, a hospital or was everything done by unsupervised immunes? Or did the immunes actually have an order of junior rank?

There are no records of Junior NCOs (JNCOs) other than the authority of office of the immunes ‘at trade’ but given the need for effective command and control there would have had to have been some grade of JNCO to assist the principales. The answer may be at the contubernia level. Each contubernia is accommodated in a pair of rooms along the barrack block. The contubernia (section) of 8 men based on the numbers in the field accommodated in a tent, would be responsible to the optio for standards of cleanliness, its messing arrangements and equipment maintenance. That cannot happen without a soldier being chosen to represent and be responsible for the section - the 18th/19th century equivalent of the ‘chosen man’ or modern Corporal. It is a reasonable assumption therefore that one of the immunes per contubernia was its de facto JNCO.

In summary, we see that overall command of the 4th Cohort of Gauls is exercised by its prefect. Routine command and control is exercised by the centurions with the general control being exercised by the principales and immunes a system of command replicated throughout military history through to today - Field officers, Company Officers, SNCOs & JNCOs.

This blog has been written as part of our Roman Holiday Project.   


P A Holder - The Roman Army in Britain

Graham Webster - The Roman Imperial Army

Adrian Goldsworthy - The Complete Roman Army

Anthony Birley - Garrison Life at Vindolanda

Robin Birley - Vindolanda

 Further Reading


David Divine - Hadrian's Wall - the NW Frontier of Rome

Adrian Goldsworthy - Hadrian’s Wall

Paul Elliott - Every Day life of a Soldier on Hadrian’s Wall

Guy De La Bedoyere - Gladius - Living, Fighting and Dying in the Roman Army