A single Polybian Roman Legion contained 10 maniples each of Velites, Hastati, Principes and Triarii. A maniple consisted of two centuries of 60 men each (or 30 in the case of Triarii). This gives 4200 infantrymen, which were accompanied by 300 cavalrymen. So with the scaling of RTW, it's simply not possible to represent a Legion (even if you assume a 1:5 or 1:10 ratio - would be easier if units were 120 men, but that would cause gameplay problems), but my Legions tend to look like this:

- 2 Generals (one the main commander 30+ years old, the other leading the cavalry 18-30 years old).
- 2 Hastati (320 men).
- 2 Principes (320 men).
- 1 Triarii (160 men).
- 2 Velites (320 men).

Regional units and Italian alae (ie the same as above, since historically they eventually fought in a very similar manner to the Romans) fill in the gaps. During deployment, I keep units in their default wide formation - deploying them in blocks as if they were individual maniples doesn't work when each unit represents five maniples.

That's my take, anyway...