Quote Originally Posted by Cloudkill
Yes, that was their normal battle tactic, but in a pinch their Triarii did form a phalanx, like when they had to fight heavy cavalry or in other defensive positions. Their pilum/gladius tactic was the standard way, but the Romans were not so inflexible that they couldn't use other ideas.
Hmmm... They might have formed up in a disciplined way, spears pointing towards the cavalry and presented a formidable front but I wouldn't call that a phalanx. And in the game they will no doubt get rank bonuses in that situation, but not as many as a phalanx.

A phalanx needs long spears, as Tamur has noted. The spears of the Triarii just aren't up to it.