Some sages believe tzitzimitls to be instruments of the gods, called down to destroy worlds whose times have come, while others claim they're the undead remains of stranded exiles from a far-off civilization of spacefaring giants. The legends that include them are ancient and fragmented, but some tell of tzitzimitls being defeated by great heroes and sealed away-though these tales imply that the enormous undead now lie buried and waiting, soon to rampage again should their tombs be breached.