"National Roman Legion"

[MARCVS PETRONIVS MAIVS]

This assumes that the Romans fought in a medieval shield wall or a scrum like the Hellanistic pikemen, or SCA heavy combat fighters, instead of the looser formations recorded by historians. If each man has more than a meter squared of space in normal formation, he won't be stepping on other feet?

Yep, which is why the "being in step" theory doesn't really apply.

Hmmn, don't we run the risk though, if we deny they fought in tight-ish formations of actually allowing the initial scenes of gladiator to take place?

I have heard time and time again that scene being scorned because it portrays one on one fighting and so on, but from the above postulations, and taking into account what has already been mentioned about the enemy taking advantage of gaps, these scenes would not seem too far fetched then.

The dense formations as seen on Trajans column and the Column of Marcus are 1.st artistic convention (compare to the Parthenon frieze) and 2nd propaganda / monumental art. IMO the dense formations were used, but rather during sieges , for defence, etc.

One might also consider the lack of possibilities for soldiers to show virtus in a too dense formation.

As I have said above, didn't the barbarians usually fight apart for exactly those reasons? (and the larger swords requiring extra swinging space). If the above theories to taken into consideration, if the cohorts did start as a shield wall, I have no doubts by the end of the battle they would not.

I thought the whole point of the effectiveness of the roman killing machine was they stayed in formation, not allowing the battle to disentegrate into small duels, where the romans would surely be maulled? (Unlike their barbarian enemies)