The Cauldron-Born were deathless warriors made from dead bodies stolen from barrow mounds by Arawn Death-Lord, and revived in the Black Crochan. They served Arawn unquestioningly, though during the events of The Book of Three, a few Cauldron-Born were also under the command of Achren, possibly because she was serving Arawn at the time.
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The deathless warriors were based in the Hall of Warriors in Annuvin, where the Crochan was also kept until its disappearance during the events of The Black Cauldron.
These deathless warriors had "livid" or "pallid" features and "lightless eyes" like stones. Their mouths were "frozen in the hideous grin of death". They wore studded bronze breastplates, heavy bronze belts, and wielded swords and black leather whips. Certain Cauldron warriors, sent on Arawn's "ruthless tasks" of reconaissance or capture, wore no helmets nor bore shields; while those deployed for battle were more heavily armored and bore both helms and shields.
The Cauldron-Born were invulnerable to all mundane weapons. A sword buried in their breast would produce only a brief halt to the deathless warrior's advance; the wound was bloodless and did no damage to the wounded Cauldron-Born. These warriors were mute, emanating a "ghostly silence", and felt no pain. In the act of their unnatural resurrection, Arawn destroyed all memory of their former selves; they could only fulfill their master's commands, and to bring others into death's cold bondage.
Their power weakened the farther and longer they stayed away from Annuvin. The Cauldon-Born were vulnerable only to the power of the magical sword Dyrnwyn, as revealed in the final volume in the series, The High King.
In the 1985 animated film, the Cauldron-Born do not exist until the Horned King -- who in this version is the main antagonist -- brings them to life with the Cauldron he has stolen from Taran and his Companions. The ghoulish sequence depicting the warriors' rebirth earned the film a PG rating.