For this reason, when playing Mid-Republican Romans, I often use the checkerboard formation (see below) which can be devastating in the right situations.
The Roman hastati (Armoured, Superior, Impact Foot, Skilled Swordsmen) are in front of two supporting BG's of triarii (hence the checkerboard) who are NOT in base to base contact with the hastati themselves. They face a rampaging warband of Gaesati (Heavy Foot, Protected, Impact Foot, Swordsmen) of 8 bases who rush into the attack.
Surely the hastati will be swept away by such a rampage?
Well, no. Because impact bonuses only apply at impact, the Gallic charge only impacts on the two front bases of the hastati. The Gaesati on each flank cannot step forward to contact the Triarii as they will no longer be in base contact with the middle group of Gaestati.
Therefore (as both are Impact Foot) and superior armour only counts in melee they nullify each others' bonuses and its a straight roll (4 vs 4) with no net POA's.
The Romans get in with 2 hits - as do the Gauls. As its a drawn melee so the death roll is at +2 (hence not worth rolling) and neither side takes a cohesion test.
The key is for the Romans to survive the impact and first melee. This is the hard part. They are overlapped on both sides (so the Gauls get 8 dice to the Roman 4) but the Romans enjoy two POA's - Skilled Swordsmen and better armour - so the Romans fight at ++ and the Gauls at --. The Gauls still have the advantage of numbers though...
They only get in 2 hits - which the Romans respond with four 3's! So the Romans win with 4 hits to 2. Luck is with them. They do not need to make a death roll and the Gauls must make a cohesion test at -2 (took more than 1HP3B and received 2 more hits than inflicted). So they need a 9 and get a 9 - they stay at Steady. They need 5 on the Death Roll and get 4. They lose a base.
This is where the checkerboard now pays off. The Roman general now moves the Triarii forward to join the melee in an overlap position (so no Impact bonuses for the Gauls here). The Gauls now face elite units (re-roll 1's and 2's) on both sides AND a superior enemy in the middle. The Triarii are Offensive Spearmen in 2 ranks and so get a +POA (and nullify the Gaul's Swordsman +POA as they are Steady). In addition, the Triarii are better armoured.
Starting from the left...
Triarii (1.3) Gauls (6,4). The Triarii re-roll the 1 and get a 4 - 2 hits to 1.
Hastati (5,4,2,1), Gauls (4,4,1). The Romans re-roll the 1 for a 2 - 2 hits to 0.
Triarii (2,1), Gauls (6,4). The Triarii re-roll both dice for 5,6! 2 hits to 1.All down the line the Romans have won the combats. The Gauls got two hits in - but against separate BG's (so in effect, had no effect at all). By contrast the Romans got in 6 hits so the Gauls automatically lose a base and face another cohesion test (again at -2). This time they roll 11! They retain cohesion but are now down to 6 bases.
The next round of melee begins.
Triarii (4,2), Gauls (1,2) - the 2 is re-rolled for a 5 - 2 hits to 0
Hastati (6,5,4,3), Gauls (5,4). 4 hits to 1
Triarii (5,3), Gauls (4,1). 2 hits to 0.
But the writing is on the wall and the next melee becomes pretty academic. The Gauls have lost 25% of their bases (-1 on cohesion test) and are likely to autobreak as they will probably lose another base this turn.
Triarii (4,1), Gauls 5. Re-roll gives a 2. 1 hit each.
Hastati (6,5,4,1), Gauls (2). 1 re-rolled to a 2. 3 hits to 0.
Triarii (6,3), Gauls (4,4). 2 hits to 0.
The Gauls take another 6 hits and lose a base. They Autobreak irrespective of any cohestion test.
Of course the Romans were lucky in that the Hastati won the initial melee but even if they'd lost and gone Disrupted, the Triarii stepping up (and therefore soaking up the Gallic hits amongst 3 BG's while inflicting all hits against 1BG) meant that the Gauls were likely to lose heavily in any respect - especially as the Romans managed to nullify the impact and then brought POA's to bear in the melee.
As a consequence the Gauls have lost one of theit best BG's - and inflicted no damage at all in return.
The Romans next movement phase can see them stepping the Triarii back again into the checkerboard. And there is another reason for this
The checkerboard formation also protects the flanks of the Roman line. If a charge impacts on the Triarii - as it hits a very narrow front it is reduced in effect. If the oppostion wish to charge the Hastati they have to go through the Triarii's ZOI - and therefore face an interception charge in their own flank.
This tactic is not restricted to the Romans - any army could use this formation to take on the opposition. But its best used against opponents with good Impact but poor melee POA's - such as the Gauls.