Battle Tactic: Bait and Switch
Use cavalry or javelin units to feint against or fire at large enemy forces. When your auxiliaries retreat, they will lure these enemy forces away from the main battle, so the main enemy force attacking your heavy legions will be reduced, perhaps even outnumbered and easily defeated. After your heavy units defeat the first half of enemy army, and the second half unsuccessfully pursues your faster light troops, you may then use the light troops to lure the enemy into an ambush set by your heavy units, or bring the heavy units forward against the rear of the enemy forces chasing your light troops.
Still a better tactic is to use light troops (Cavalry or Javelins) to repeatedly lure small sections of the enemy army in different directions, so they become scattered into fragments which may be defeated in detail by your united heavy units. The faster light units may even themselves scatter to attract the enemy sub units along varying directions. Your fast light troops can quickly reunite to strike each fragment one at a time, before the slower enemy fragments may reunite to oppose them. Cavalry are especially useful here, since one single unit, because of it's speed, can feint against, and attract many enemy forces, toward different locations in a very short time. These scattered fragments can then be overwhelmed by united Heavy infantry and javelin forces
This tactic resembles what Reckless Rodent calls: Divide and Conquer
Another little tactic which I find particularly useful against large Carthaginian armies is the "divide and conquer" tactic. Here, you form your legions and javelins as described above, and then you advance with 1 of your javelin cohorts. These javelins get within shootng dostance of the enemy, and let fly. This draws a group of the Carthaginians away from the bulk of their army. You can then lead this group back to the main body of your army, where they can be annhilated. This way, you find yourself faced with fewer enemies when the main Carthaginian army arrives.
[Angel Reckless Rodent]
See also: Bait and Bombard