As you progress up the technology tree and through the Ages, other civilizations will be quick to make demands or aggressions against your blossoming empire. In this section we'll examine a few tricks of the trade such as forming strong unit stacks and using game elements like terrain and movement points. After your civilization has matured, and you can generate a healthy amount of resources, it's time to begin constructing an offensive and defensive force. A stack is a collective force that moves together much like an army. While the melee units engage each other from the front line, the ranged units sit safely in the rear and fire their weapons without worry of immediate retaliation.
Ranged units are much weaker than melee units.
Another fine addition to your unit stack is bombardment units, such as artillery or cannons. These units can be placed outside the stack and fire on the enemy force from a safe distance, working down your opponent before the melee and ranged unit take their shots. Don't think all the units you construct should be sent on offense. Without an adequate defense, a lowly barbarian could waltz in and dismantle your once proud, but defenseless, town. Keep several units inside each city, especially early in the game.