"The Unsullied are not men. Death means nothing to them."
―Missandei to Daenerys
The Unsullied are elite warrior-eunuchs bred and trained in Astapor, one of the three major cities of Slaver's Bay. They are slave-soldiers famed for their skills and discipline in battle. They are also often purchased from Astapor by some of the Free Cities, such as Qohor.
Unsullied battle tactics are based on the legions of the old Ghiscari Empire, involving large groups of them fighting in lock-step phalanxes using spear and shield, though they are also trained to use shortswords for close-quarters combat. Slave-eunuchs who have been trained from birth to fight, the Unsullied are renowned for their utter discipline on the battlefield, both in their usage of incredibly coordinated large unit phalanx formations, and because they will never break in the face of overwhelming odds, even to the point of death.
Unsullied training begins when the boys are five years old: some were selected to be Unsullied as infants and castrated then, though any slave boy up to the age of five may be later selected to be made into an Unsullied, and then castrated. For over a decade until they are full-grown, they train from dawn to dusk until they have mastered the short sword, shield, and three lengths of spear, as well as their training to fight together as organized phalanxes. The training regimen is utterly brutal, and because of this, only one out of every four boys survives until the end.
Because they are eunuchs, the Unsullied will not succumb to bloodthirsty or sexual urges in the midst of battle; their actions will only go as far as what they have been ordered to do, and nothing more. The Unsullied also seem resistant and even immune to pain. However, Unsullied do possess emotions and can show anger.