An army is comprised of different land units.
Archers – Can assault, prefer to fight from the second row and can be built by anyone. Are good versus infantry, but weaker against cavalry. Cheap and fast to build.
Camels – Fights on flanks and require the camel trade-goods. Are quick to build and move quickly. Strong versus lightly armored types.
Cavalry – Fights on flanks and require the horse trade-goods. Are more expensive to build and move quickly. Countered by heavy infantry and war elephants, but are very good against everything else.
Chariots – Can be built if Celtic or Mauryan. Cheap to build and are very good against light infantry, but weaker against other units.
Heavy Infantry – Can assault and require the iron trade-goods. Are expensive but are really good against cavalry, light infantry and chariots.
Horse Archers – Fights from the second row and require the steppe horse trade-goods. Cost is similar to cavalry, and are strong against slower moving units.
Light Cavalry – Fights on flanks and require the horse trade-goods. Not very expensive to build and move very quickly. Weak against most units but strong against archers and light infantry.
Light Infantry – Also known as militia, these units can assault and be built by everyone. They are cheap and quick to build, but weak against every other type of unit.
War Elephants – Requires the elephant trade-goods. Are very expensive to build but are very good against units that can not quickly run away.