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The mountains of Japan’s Yamagata prefecture are considered sacred by the Buddhists in the region. These holy sites are sparsely populated, their forests interrupted only occasionally by isolated Buddhist temples. Many of the men serving in the temples come seeking solitude and an escape from the modern world. They were probably a bit startled, then, when a group of scientists and historians showed up in 1960 and asked to see their mummies.

The year before, several researchers investigating rumors of local mummies had discovered six mummified Buddhist monks in five temples in Yamagata prefecture. Soon after the discovery, several Japanese universities formed the Investigating Committee for Mummies to study them. The mummies were each kept on display in a place of honor in the temples, and were maintained by the temple monks. Unlike the Egyptian mummies that are most familiar to the Western world, these Japanese mummies were not wrapped in cloth. Instead, they were dressed in monks’ robes, their dried, leathery skin visible on their faces and hands.

Mummies were not unheard of in Japan. In fact, four leaders of the Fujiwara tribe had been mummified in the twelfth century and were still kept in a great golden temple hall in northeastern Japan. But mummification is a tricky business, especially in a climate as humid as Japan’s. The researchers hoped to examine the temple mummies to uncover the details of this specific mummification process.

To prevent bacteria, insects, and fungi from decomposing the mummy, the mummifier usually begins by extracting the internal organs to remove the most tempting food sources for the critters of decay. So when the researchers began examining the Yamagata mummies, they were startled to find that the monks’ internal organs were still intact, and had begun to dry before death. Close examination of the temple records revealed that this live-mummification wasn’t some kind of torture or ritual murder, but rather ritual suicide. These monks had mummified themselves.

The mummified monks of the Yamagata province had belonged to the Shingon school of Buddhism, which combined esoteric Buddhism with native Shinto beliefs. These Shingon monks practiced extreme asceticism, believing that physical deprivation allowed them to see beyond the illusion of the physical world. They would meditate under icy waterfalls or walk across hot coals to practice ignoring their physical selves.

These monks also believed deeply in self-sacrifice in service to others. This manifested in a lot of the usual community service: feeding the poor, caring for the elderly, treating the sick. But they also believed that their sacrifices could serve the community through spiritual means. For example, in the late 18th century the Shingon monk Tetsumonkai travelled through what is now Tokyo during the outbreak of an eye disease that caused blindness. When his herbal remedies had no effect on the epidemic, Tetsumonkai cut out his left eye and threw it in the Sumida River while praying for the end of the epidemic, believing that his sacrifice commanded a higher level of respect and attention from the gods.

The monks who mummified themselves (including Tetsumonkai) considered their death an act of redemption and salvation for humankind. Their suffering prior to death allowed them to go to the Tusita Heaven, one of several Buddhist heavens whose residents enjoy extremely long life spans before they reenter the cycle of reincarnation. The monks believed their sacrifice would allow them to live in the Tusita Heaven for 1.6 million years, with the power to grant requests and protect the humans on Earth. But they also believed that this spiritual power only lasted as long as their physical bodies remained to tie them to the Earth, so it was vital that their bodies be preserved through mummification.

A monk who chose to perform self-mummification, or sokushinbutsu, began by abstaining from grains and cereals, eating only fruits and nuts for one thousand days. He spent this nearly three years meditating and continuing to perform service to the temple and community. Then for the next thousand days the monk ate only pine needles and bark. By the end of the two thousand days of fasting, the monk’s body had wasted away through starvation and dehydration. While this satisfied the requirement for suffering, it also started the process of mummification by removing excess fat and water, which would otherwise attract bacteria and insects after death. Some of the monks drank tea made from the bark of the urushi tree during their fast. Also known as the Japanese Varnish Tree, its sap is normally used to make a lacquer varnish, and it contains the same abrasive chemical that makes poison ivy so unpleasant. Urushi is so toxic that even its vapor can cause a rash, and it remains in the body after death. Drinking urushi tea served to hasten the monk towards death as well as make his body even less hospitable to insects.

Finally, the monk would enter a cramped, specially built tomb and sit in meditation as his acolytes sealed him in, leaving a small tube to allow air to enter. He spent his last days in sitting in meditation, ringing a bell occasionally to signal to those outside that he was still alive. When the bell stopped, the acolytes removed the breathing tube and sealed the tomb completely. After a thousand days, his followers opened the tomb and examined the body. If there was no sign of decay, the monk had achieved sokushinbutsu and was placed in a temple and worshipped as a Living Buddha. If not, he was reburied with great honor for the attempt.

The first known attempt of sokushinbutsu was in 1081 by a monk named Shōjin, but it was unsuccessful and his body decayed. Over one hundred monks may have made the attempt since then, but only around two dozen in Yamagata and surrounding prefectures have succeeded. The procedure for self-mummification evolved through trial-and-error, and even monks who followed the same tortuous steps as successful sokushinbutsu monks could fail for no discernible reason, losing their chance at immortality Tusita Heaven after years of painful asceticism.

Monks in Yamagata had a particularly high success rate compared to monks in other regions, especially the monks who drank water from the sacred spring on Yudono Mountain during the years leading up to their death. Researchers from the Investigating Committee for Mummies in Japan analyzed the water from the Yudono spring and found near-fatal levels of arsenic. Aside from acting as a poison, arsenic also remains in the body after death, performing the same task as urushi tea and discouraging insects from taking up residence.

In 1877, Emperor Meiji outlawed self-mummification in Japan. The law prohibited anyone from opening the tomb of a monk who had attempted sokushinbutsu, unless the monk had entered the tomb before the law was enacted. The one-eyed monk Tetsuryūkai had been preparing for sokushinbutsu for years when the law was enacted, so he decided to complete his journey anyway and was sealed in the tomb in 1878. At the appointed time after his death, his followers snuck out to his tomb in the middle of the night and disinterred him in secret. They were overjoyed to discover that he had achieved sokushinbutsu, but then they realized they faced a great dilemma. They couldn’t put his body on display in the temple without admitting that they had broken the law by opening his tomb. Ultimately, they decided to alter the temple records to list Tetsuryūkai’s date of death as 1862⁠—prior to the ban⁠—and enshrined him at Nangaku Temple, where he remains to this day.

Part of the Yamadera mountain temple complex, where Sokushinbutsu was practiced.
Part of the Yamadera mountain temple complex, where Sokushinbutsu was practiced.

Tetsuryūkai is the last known successful sokushinbutsu mummy. Other monks who had begun fasting in preparation for sokushinbutsu when the ban was passed abandoned their attempts. They eventually died of natural causes and were cremated, but they are honored with statues in several temples throughout Japan. The remains of some of the monks who achieved sokushinbutsu have been lost in fires or other disasters, but sixteen can still be seen in temples in Japan today. Each sits in the lotus position in which he died, dressed in traditional robes. Their faces are eyeless, grinning skeletons with darkened, leathery skin stretched across their skulls. Their bony hands clutch prayer beads or rest gently in their laps. Worshippers visit with prayers and petitions in the hopes that the sokushinbutsu monks will intervene with a miracle to grant their requests.

Due to the large number of known attempts at self-mummification in Japan’s history, and the secluded manner in which the process was practiced, it is possible that other successfully mummified monks are still buried in their tombs in the mountains of Yamagata, their locations lost to time and their sacrifice forgotten.