with solid rock or permafrost underlying the surface. The customs are first recorded in an indigenous 12th-century Buddhist treatise, which is colloquially known as the Book of the Dead (Bardo Thodol). Tibetan tantricism appears to have influenced the procedure. The body is cut up according to instructions given by a lama or adept. Mongolians traditionally buried their dead (sometimes with human or animal sacrifice for the wealthier chieftains) but the Tümed adopted sky burial following their conversion to Tibetan Buddhism under Altan Khan during the Ming dynasty and other banners subsequently converted under the Manchu Qing dynasty. Sky burial was initially treated as a primitive superstition and sanitation concern by the Communist governments of both the PRC and Mongolia; both states closed many temples and China banned the practice completely from the Cultural Revolution of the late 1960s until the 1980s. During this period, sky burials were considered among the Four Olds, which was the umbrella term used by Communists to describe anti-proletarian customs, cultures and ideas. As a result of these policies, many corpses would simply be buried or thrown in rivers. Many families believed the souls of these people would never escape purgatory and became ghosts. Sky burial nonetheless continued to be practiced in rural areas and has even received official protection in recent years. However, the practice continues to diminish for a number of reasons, including restrictions on its practice near urban areas and diminishing numbers of vultures in rural districts. Finally, Tibetan practice holds that the yak carrying the body to the charnel grounds should be set free, making the rite much more expensive than a service at a crematorium. Purpose and meaning For Tibetan Buddhists, sky burial and cremation are templates of instructional teaching on the impermanence of life. Jhator is considered an act of generosity on the part of the deceased, since the deceased and their surviving relatives are providing food to sustain living beings. Such generosity and compassion for all beings are important virtues in Buddhism. Although some observers have suggested that jhator is also meant to unite the deceased person with the sky or sacred realm, this does not seem consistent with most of the knowledgeable commentary and eyewitness reports, which indicate that Tibetans believe that at this point life has completely left the body and the body contains nothing more than simple flesh. Only people who directly know the deceased usually