battle tactic

It really depends on who you are fighting. Every nation has their own type of unit, each with its own advantages and pitfalls. Look at the Greeks. Fighting against the Caucses states (Pontus, Armenia) sucks because they use horse archers, who just pick off a phalanx.

I mostly play as the Romans, so I have a good feel as to what should be used for what.

Pre-Marian Reforms:
Keep Veletes in the front to pepper the enemy as they advance, then they retreat as reserves.

Put Pricipes and Hastani at the core to fight off the charging enemy, and to use pli to demoralize my foe.

Keep Triarri on the outside to protect against a cavalry unit outflanking the main line.

Naturally, keep the archers in the rear to keep them alive

Hide your cavalry (not general) somewhere close by. Right when the enemy is thinking about routing, "convince" him to do so with a timley cavalry charge at their flanks or rear.

Post-Marian reforms.

Keep Auxilia on the flanks. Their spears work well against horses, and their cheap cost makes them expendable.

Put Legionary First Cohort in the middle of the infantry rank. The eagle symbol that the leader carries is a big morale boost for surronding troops.

Put the heavy guys, like Praetorians and Urban Cohorts in the front where they can do the most damage. Then put lighter early legionary cohorts slightly to the rear as a reserve to exploit a breakthrough.

I always keep a handful of cavalry in the rear incase of an emergency.

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Dont forget to use mercs! Barbarian Infantry have a bonus fighting Germania, Gaul, and British troops, etc... They have experience in the field, and are a great way to keep your numbers up.

Hell, some of them are better in their job then their Roman counterparts. The Cretian Archers fire faster, farther, and with more accuracy than Roman Archers or Archer Auxilia.:juggle2: