By allowing vultures to consume the corpse, it is both one final charitable act and an assurance that evil spirits won’t find an empty vessel to takeover.

These circular stone buildings reach 18 feet into the air and measure 300 feet in circumference. Each dakhma holds around 250 bodies. On the top are three circles: the outer was reserved for men, the middle for women, and the central circle was for children. After no flesh was left, bones would be collected and stored in the central pit of the structure, or in a private ossuary. They are outfitted with an iron door and four towers that connect with channels to the center and serve to drain and filter any washed away matter.  After no flesh was left, bones would be collected and stored in the central pit of the structure.

Many of these sacrificial structures still dot the barren landscape of Yazd, Iran, although the practice has forcibly died out. In the 1970s, as the urban sprawl crept toward the ancient sites, ceremonial use of the towers was called a health risk and forbidden entirely.

Instead of maintain thousands of years of ancestral tradition, the Zoroastrians—adherents of one of the oldest monotheistic religions—began entombing their dead in concrete coffins, believing it would block outside contaminants.

Meanwhile, in India, a Zoroastrian sect known as the Parsis still practices traditional burial methods. The group originally fled from persecution in Iran, then Persia, starting in the seventh century.

In a swanky neighborhood of Mumbai known as Malabar Hill, the Parsis have dotted a 300-year-old hilltop garden with Towers of Silence. There, they carry on a centuries’ old tradition in peace. But recently their ritual has come under threat, not from the government or surrounding neighbors, but due to a lack of vultures, according to a recent Guardian article.

In the 1990s, a drug given to livestock killed off 95 percent of the vulture population. And India’s 61,000-strong Zoroastrians—who are dying off faster than they’re reproducing—are panicked about the failure of their body disposal system.

A proposed vulture breeding program has failed to produce quick results, so instead they’ve been using solar power to quicken decomposition. Results have been unsatisfactory. Rather than a 30-minute vulture feast, bodies can take weeks to disintegrate in solar power. This unappetizing sight—visible from nearby high-rises—has already prompted one tower to shut down and air purifiers to be installed in the others.

Death by air has already reached its demise in Iran and is nearing a death rattle in India. Before long, the Towers of Silence will live up to their name.

Nina Strochlic’s essay “Where Old and New Worlds Collide” appears in National Geographic’s Journeys Home, on sale Feb. 3.

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