Roman Battle Formations Mid Republic to Late Rep.

[Q Rutilius]

Crispus: "We do see a variety of tactics used in the examples cited above. We see gaps left for cavalry to ride through; we see narrow gaps between what appear to be cohesive units; we see gaps filled with skirmishing soldiers used as ruses; we see multiple battle lines and we see apparently independent cohorts. I don't think there is much chance of either of you managing to set all of these things within a single tactical layout. Rather, they are all examples of tactics Roman commanders could employ in response to the tactical demands, using the skill-sets of the soldiers at their disposal." (Sorry, I could not make the quote thing work.)

This, I think, is the nub of it. It is reasonable to suppose a number of tactical layouts. How else, does one explain the various accounts of Caesar et al?

Gaps could have been left, although I doubt it. But, if the terrain is rough enough, if the enemy has certain characteristics, i.e. they fought in small independent groups too, then gaps in the line might make sense. Which brings us back to Crispus' point; no one formation fits all possibilites.
(I think I am reading you correctly here.)

I might add that I have often thought how similar or dissimilar Roman formations and tactics were compared to the formations and tactics of the other Italians. A book describing warfare as waged by the Samnites, Ligurians etc would be darned interesting, but I know of no such book. If, I say if, there is good evidence that say the Samnites fought with gaps, I'd be much more inclined to think that at least some of the time the Romans did too.