The Mercenary is the second unlocked unit in Early Middle Ages. It is trainable in Mercenary Barracks (3x3) after having researched the Mercenaries technology. Just like its predecessor, the Soldier, it has a balanced attack and defense value, an attack bonus of 5 against Heavy Cavalry (fast) unit, a defense bonus of 3 in bushes and 5 in forests. Bronze age units are almost no match for them.
The Mercenary is not the first unlocked military unit in Early Middle Ages.
Mercenaries are a balanced unit of the age. They are good against any other unit except Armored Infantry, which has a defense and attack bonus against them.
They can be used to attack Mounted Archers, which have low attack for a ranged unit in the EMA, and two hit them. The AI or computer usually sends Mounted Archers to the player's side of the map right at the beginning of the battle, allowing the Mercenary to attack it.
They also can be used for attacking Heavy Cavalry, especially since they have an attack bonus against them. They also have a defense bonus against Heavy Cavalry, meaning that it would take 3 hits or more for Heavy Cavalry to kill a Mercenary in a forest.
They also can withstand Catapults, the same age artillery unit, however, it is recommended to have the Mercenary in cover, to minimize the chances of the Catapult of doing three hitpoints of damage to the Mercenary. Even with one hitpoint, Mercenaries can two hit kill a Catapult, and even one hit them if the sector has been infiltrated.