Zoroastrian theology treats earth, fire and water as sacred creations that must not be contaminated by contact with a corpse, which the tradition regards as a locus of nasu, a spiritual impurity or corrupting force believed to take hold of the body at the moment of death, a concern the tradition treats as ritually and cosmologically serious rather than merely practical.
Burial and cremation, the two most common funerary methods elsewhere in the world, are both therefore judged to defile a sacred element, earth or fire, and traditional Zoroastrian practice developed dakhma exposure, dokhmenashini, as the method that avoids both, exposing the body instead in a specially constructed dakhma, a raised circular structure with no roof, popularly known in English as a tower of silence, so that the flesh is consumed by scavenging birds and the sun rather than committed to earth, fire or water. The remains, once skeletonised, were traditionally understood to be sufficiently free of nasu that the bones could then be placed without further concern in a central ossuary pit within the structure itself, completing the funerary process without any of the sacred elements having been directly touched by the corrupting matter of death.