The army was divided into LEGIONS which, while sometime less, were meant to be 6000 soldiers.

The LEGIONS were commanded by 6 TRIBUNI who took turns being in charge. ( ( The chief commander mentioned in Acts 21:31)

The LEGIONS were divided into ten sections called COHORTS (Mentioned in Acts 10:1) Each COHORT contained 600 men.

Each COHORT was divided into 3 MANIPLES of 200 men each.

Each MANIPLE was divided into 2 CENTURIES usually of 100 men each. Even though as the legions grew and shrunk, the numbers would vary. Each CENTURY was commanded by a CENTURION, of which there are many mentioned in scripture. (Acts 10:1, 22 Matthew 8:5, 27:54)

So the breakdown of command looked like this:

Legion (6000 men) --Cohort (600 men) --Maniple (200 men) --Century (100 men)

--Cohort --Maniple --Century

--Cohort --Maniple

--Cohort

--Cohort

--Cohort

--Cohort

--Cohort

--Cohort

--Cohort

There were also bands of special volunteers two of which were mentioned in scripture:

Italian Band (Acts 10:1) Augustus Band (Which protected the Emperor) (Acts 27:1)