The flexibility of the legions is something we're trying to simulate in Rome. As an example, because of their pila they'll be useful both in melee and raged roles. We're also planning to let you change their marching order so you can force-march them somewhere to go faster, or put them in a marching order that leaves them more open to attack, but allows them to carry more supplies. In an earlier design we also wanted to be able to separate the legions into cohorts (Caesar actually mentions this more often than you might be aware) but unfortunately that was a feature we had to drop in order to keep our timeline reasonable.

And the auxiliaries are definitely going to be extraordinarily important. Caesar had few legions, and the legions he had were constantly undermanned. On top of that, the post-Marian Romans simply did not have javelineers, archers, skirmishers, or cavalry, so the only way to fill those roles is with auxiliaries.

The flexibility of the legions came from more standardized equipment and extensive training, with extra emphasis on how to behave and respond to various situations. This allowed new recruits to more easily assimilate into the legion. i.e. Everyone knew what to teach them and the recruit quickly learned what to do, gaining confidence.

The strength of this fluid combination of cohesion and flexibility, was the redundancy that showed itself when a legion was faced with tactical setback and defeat, or when caught in a strategic bind. The training and confidence (moral) of the legionaries, enabled them to recover from a setback and regroup, rather than rout from a tactical defeat. They knew what to do, even if their immediate commander was killed. Contingency plans kept units from disintegrating and men from routing under duress.

Fighting in unfamiliar territory, I suspect that the legions were frequently caught off guard (under informed and/or underfed and overreaching), sustaining many minor defeats that they were able to recoil and recover from. Thanks to this redundancy, they survived to fight again.

A good analogy is that fighting a band of skilled warriors was like dealing with an egg. However tough, once you broke through the shell, it was all but over and they would run (pun intended). On the other hand, fighting a legion was like dealing with an onion. You'd have to peal away layer upon layer...

Caesar was far less likely to write about tactical defeats or strategic setbacks, unless they were too large to ignore when reporting back to Rome. He was also less likely to give credit to his Gallic/German auxiliaries, who were invaluable in reconnaissance, procuring supplies from the locals and fighting. If it lost its lines-of-communication, and more importantly, supply, a legion was vulnerable to disruption and defeat.

It's this level of legionary warfare that we are trying to recreate in Hegemony Rome. The level of unit diversity that we can include, will depend on what our small team of artists and programmers can put together after the main concepts have been addressed.

Anyway, we'll try. :)

Unfortunately, the triplex acies were done away with after the Marian reforms. As far as the flying wedge goes, it's certainly likely that we'll include it, especially since we implemented it in the first game (it's called the "Chevron Formation" there). I can't say for certain, though, because we're doing some work on the formations to make them more useful, and there's going to have to be a bit of experimentation with that new system, so I won't know for sure until that's done.

We do actually own a number of Osprey books; they are fantastic. Our artists especially love them for their visual reference.

Like I said, we're making sure that one of the strengths of the legions is their flexibility, but we always have to be careful not to make them too flexible, because at some point that starts to undermine the importance of the auxiliaries. Considering how often Caesar seemed to use his auxiliaries as skirmishers — and keep in mind that he gave credit to his auxiliaries in this role, even though he always preferred to give credit to his legions — it's unlikely that we'll promote using legions as skirmishers.

If we were doing a game about the civil war, on the other hand, I would be far more inclined to implement something similar, since Caesar had far fewer auxiliaries and had to get creative with his legions. He even used them as pikemen against Pompey's cavalry!

Definitely yes to the cavalry. As far as the heavy infantry goes, we're undecided yet whether we'll split the auxiliary infantry into light/heavy or not. Depends how it plays.