Traditional Mexican barbacoa — the slow-cooking of a whole head, whole sheep, or whole goat in an underground pit lined with heated volcanic stones and maguey (agave) leaves — is the Mesoamerican counterpart to the Peruvian pachamanca (PE-22). The maguey leaves add a specific aromatic (saponin and other compounds from the agave plant), protect the meat from direct stone contact, and contribute moisture through their own water content.
Mexico: The Cookbook