Legatus Legionis
The legati Augusti legionis (legionary commanders) were senators, ex-praetors around thirty years of age who typically
served a 3 (sometimes up to 7)  year tour of duty.
Legati Augusti pro-praetore governed Imperial provinces. Those
provinces with one legion were commanded by ex-praetors (who also acted as legionary COs) and those with more by ex-
consuls. The latter commanded all of the provincial legates and their troops (i.e., Britain had four legions).

Tribunus Laticlavius
The second-in-command, a tribune and a senatorial designate around the age of 25, served for one year. Although
command ‘technically’ defaulted to the
Tribunus Laticlavius in the absence of the Legatus, it is more probable that the
Praefectus and Tribuni Angusticlavii (see below) assumed control.

Tribuni Angusticlavii
Each legion had five Tribuni Angusticlavii, equestrian tribunes, who served 3-4 years and then assumed command of a
cavalry ala. They were generally young men (former magistrates and/or auxiliary
cohors peditata/equitata commanders).
During the Republic each tribune commanded two cohorts but in the Principate they occupied staff positions with an
administrative/judicial focus.
Tacitus reported that they monitored the performance/reliability of the centurions. Their staff (
officium) was comprised of
clerks (
cornicularii and secutores) without military responsibilities who recorded casualties, maintained current lists of
men serving, processed furlough applications and dispensed discharges to retiring veterans. Tribunes often commanded
vexillations, detachments of one or more cohorts on special assignments.

Tribuni Semestres were part of H.Q. staff and served 6 months before resuming civilian life. Following the Flavian era they
were placed in direct command of the legion’s 120 man cavalry contingent (four
turmae of 30 horsemen). The cavalrymen
were ranked as non-combatants along with the headquarters staff. They were attached to specific centuries (as opposed
to forming individual units) and served as messengers and scouts.

Praefectus Castrorum
The third-in-command was an equestrian,  a former head centurion in his late 50s with 30 plus years of experience. He
was basically a quartermaster responsible for choosing camp sites and overseeing their construction inclusive of
entrenchments. He inspected tent lines in temporary camps. During war he supervised the legion’s baggage train, and if
siege operations were anticipated he managed the battering rams and ammunition supplies. In permanent installations
he oversaw the construction of barracks-blocks, internal buildings, wells and aqueducts.

He was the officer in command of the doctors (
medici), the surveyors (mensores) and the horologiarius, the man
responsible for the camp clock. He oversaw the supply of construction and surveying equipment, furnishings, fabrica
supplies (inclusive of wood, iron and coal) and medical equipment for the legion’s hospital (

Primus Pilus
The fourth-in-command was the senior centurion and leader of the 1st century of the 1st cohort. He held his post for one
year. Parker believes that there were two primi pili, one who commanded troops in the first cohort and one who served in
the Legion’s headquarters.

The centurion commanding the second century of the first cohort was next in line, and he was responsible for the
headquarters’ staff as well as  training. Ranked below him were the remaining centurions of the first cohort in the following
order -
hastatus, princeps posterior and hastatus posterior.


He carried the legion’s silver (subsequently gilded) eagle and ranked just below a centurion. He was entrusted with the
legion’s pay chest.

Principales and Immunes:
Below the rank of centurion men were designated as either principales or immunes. Principales assisted the centurions
and were exempt from normal fatigues (
optio, signifer and tesserarius). Immunes, men who were excused from regular
fatigues by virtue of special skills (blacksmiths, carpenters, surveyors, medical assistants, etc.),  comprised almost 20% of
each unit.

Centurions in cohorts 2-9 were equal in rank with seniority determined by years of service. They were recognized by their
transverse helmet crests, swords worn on the left and their swagger sticks (
vitus) with which they dispensed discipline.
They typically rode when a legion was on the march. Centurions tended to die in service as opposed to retiring to civilian

The standard bearers handled the paperwork at century level. Vegetius says that the garrison was managed by the
signiferi who were directly responsible for finances. They recorded financial transactions, issued receipts, documented
account activity and dispensed pay.

He was a ‘chosen man’, a centurion-in-training who assumed field command if the unit's centurion was incapacitated or
killed. He carried a staff of office known as a

The tesserarius controlled the daily watchword and was responsible for sentries and other fatigues.

Custos Armorum:
He was responsible for centurial equipment, repairs, and weapons.

A century was composed of 10 mess units (contubernia) of six to ten men who shared a tent and a mule; each was
commanded by a

The basic foot soldier served for 20-25 years (depending upon the time period).
Army  - Command Structure
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