Usually mummification starts after you die. For some Buddhist monks, however, the process began years before you actually passed away.
These monks believed the path to immortality began by eating nothing but nuts and seeds and exercising vigorously to rid themselves of all body fat. Then, after three years, they would drink a poisonous tea that would cause them to violently purge themselves, removing moisture from inside their bodies while also killing off any internal parasites that might otherwise rot their flesh.
At last, they would wall themselves into a small, closed-off stone tomb, assume the lotus position, and simply wait to die, ringing a bell each day to let people outside know they were still alive. When the bell stopped ringing, everyone knew the monk inside was dead and the mummification process was complete.
Unfortunately, most who attempted this ritual were not successful, as opened tombs have revealed. Their corpses showed signs of decay. However, the bodies of those who achieved their goal were removed, put on display, and venerated.