Changes of Roman Legionaries from Republic to Empire

Good morning,

With my usual group of players, we were wondering about the changes in the army lists from Republican Roman to Empire.
The Roman legionaries in the three Republican army lists have two enjoyable advantages: forming large units and being able to interpenetrate other FP. But these disappear in the Roman empire lists, which make the imperial legionaries seem more fragile in comparison to there republican counterparts (especially when they have to face more mobile and/or numerous armies).
Would anyone have an idea about the historical and/or gameplay reasons underpinning these changes?

Thanks!

I think it's really for Lorenzo to answer your specific army list query.
I'm responding as I think your query may have been prompted by mismatched armies in your case good quality A class romans being slaughtered by large unit warband armies.
We recently played a couple of 600pt battles of Caesarian Romans versus FP gallic warband armies. The large units Gauls are significantly cheaper than single rank Romans so outnumbered the romans and had longer front line, could afford better generals and more skirmishers. Even with good die rolls the Romans in both games had no chance.
With this result in mind we've just played twice a refight of Marius's battle of Vercellae 'Cimbrian Wars'. The Roman army was 670pts and the Cimbrian warband army 460pts. The first battle again a fairly easy Cimbrian win although the roman die weren't good. The second game was a roman win by the narrowest of margins.
Maybe it would be worth you giving it ago with the Romans having 50% approx. more points against warband armies to see if it gives you a more balanced game.
Would be interesting to here from anybody else if they've come across other mismatches of equally pointed armies and what adjustments were made to give a playable game.

Thanks for your reply!

Indeed, we also regularly play Republican Romans vs. Gauls. The latter often win, though it's rarely an easy game, especially if Romans use large units. I never played against them, but apparently Numidians are also quite a nightmare to face (for anyone, according to what I heard).
So I am not sure whether it is a problem of giving more points to the Romans, or finding the way to counter all the lighter and mobile troops thay can face (with more allied troops? a particular deployment?). In any case, it turns out to be more difficult than expected to play FP armies... And the option of having large units seems to be a "must" if you want your legions to hold.

The Caesarian list 105-25BC which we were fighting is the 1st of the Roman lists that can't use large units. We played the game 4 times with the points variation and the score is 2 all so seems to work for us against non large units of romans.
We have encounter several miss matches between historical opponents and before the troops are put away we try to resolve issues to make the games playable. Would be good to hear from others who've encountered similar issues with other armies and how they were overcome.
What are the armies giving your romans a hard time?

well, Large Units are basically more easy to use, they rely on endurance and front charge. Roman should outmanouvre warbands and make a good use of light troops and terrain (also artillery can help).

Has everyone forgotten how bad warbands were in Impetus 1 already? Warbands were auto-lose vs Romans every time I ever played. Now it is much more balanced. and warbands are properly scary. Perhaps the changed Impetuous rule is a bit too good is my only comment.

Also pretty much every battle in Caesar's Gallic Wars reads something like "We built fortifications and the Gauls attacked us" So use fortifications and artillery.

Also Romans routinely cheated historically by taking 10,000 points to a 500 point matchup . . .

They may of cheated but those points should give a pretty fair game in impetus 2. HaHa

Thank you all for these replies, it gives a lot of food for thought.

This is also actually one of the things I personally like in Impetus: you can't be sure of anything if you basically play two lines of FP and charge forward. The manoeuvre is really an important part of the game!

@ Stecal: I can actually remember winning games with Gauls against Romans in Impetus 1 (although the compulsory forward moves were indeed hard to handle, unless placing forests all over the table to block lines of sight...).
We never tried fortifications, but perhaps we will now...