The Roman Army

A legion was 5000 to 6000 men. It was divided into 10 cohorts of around 500 men. Each cohort was divided into centuries 100 strong.

In the first century AD Rome had 30 legions made up of citizen soldiers. It is not clear how many auxiliary forces were used but they were structured as below in the first 200 years in Scotland

Cohors peditia (Infantry)

480 to 600 men (all infantry)
6 centuriae of 80 to 100 men

Cohors peditia milliairia (Infantry)

800 to 1000 men (all infantry)
10 centuriae of 80 to 100 men

Cohors equitata (mixed unit)

600 to 720 men
120 cavalry (4 turmae) and 480 to 600 infantry (6 centuriae)
Suited to a range of tasks. The cavalrymen did not enjoy the same status as their counterparts in the alae

Cohors equitata milliaria (mixed unit)

1040 men
800 infantry (10 centuriae of 80) men and 240 cavalry (8 turmae of 30 men)

Ala quingenaria (Cavalry regiment)

480 men (all cavalry)
16 turmae of 30 cavalrymen

Ala milliaria (Cavalry regiment)

720 to 864 men (all cavalry)
24 turmae of 30 to 36 cavalrymen