Gigantes are feral giants kept by the barbarians as pets and beasts of war.
They have various attacks they use on their enemies. One of their attacks is grabbing a target and then throwing them a fair distance dealing some damage.
They are extremely aggressive and their attacks will knock down anyone, even allies in their path. Multiple Gigantes will deal damage to each other, and in waves of many, they can unintentionally kill each other.
Some Gigantes wield clubs which allow them to inflict more damage on grabbed units (instantly killing allied hoplites). They are also able to take much more punishment than their unarmed counterpart.
It is possible to find a chest containing an Allied Gigante behind Beowulf's troops after taking his hammer. The Gigante may be put to use by equipping it in the arena menu.