orientaltiger:

The ancient Zoroastrian tradition tells of how human flesh, once dead and decomposing, is so unclean it will pollute everything it touches. In acts of elaborate ritual the dead would be carted out into the forbidding desert by thenasellars, ritual pallbearers of Zoroastrianism. The dead bodies were taken up winding slopes up to the Towers of Silence. A Tower of Silence, known as dakhma in the sacred avestan tongue, is a large, cylindrical structure laid in concentric circles surrounding a center pit. Its sole purpose was to leave dead bodies exposed to the searing desert conditions and be eaten by birds of prey.