Quote Originally Posted by Spino
I simply don't believe well trained, disciplined veterans fighting with large shields and 3 meter long spears
3 meters long? I have always gotten the feeling that they were in fact no more than 2 meters (Romans being around 1.60 meters it would seem much longer).
Also everything I have seen of hte Triarii, depicts them as wielding the spears in a semi-underhand fashion (lets call it couched), which by its nature excludes a phalanx, as the shields can't get all that close without locking the spears in place.
Now that might very well be wrong.

But we do not consider the Persian Applebearers as formed up in a phalanx, despite the fact that they carried large shields and long spears... And these guys for certainty fought with the overhand style like the hoplites (lets be classical here for a moment).
Also the Roman formation wasn't as rigid, each man was allowed a certain amount of freedom, such as helping his friends over there if they get attacked by cavalry, in the hoplite phalanx that was frowned upon, and could even be hard to do (locking of shields would make it hard to disentangle).