(via Archaeologists discovered a new papyrus of Egyptian Book of the Dead | Ars Technica)
One of the most famous spells is the “Weighing of the Heart” (designated 125 by scholars), dating to around 1475 BCE, by which time copies of the Book of the Dead were commonly written on papyrus. Anubis would lead the deceased before Osiris, where they would swear they had not committed any of 42 listed “sins,” and their heart was weighed on a pair of scales against a feather to determine if they were worthy of a place in the afterlife. (Those who watched Moon Knight will remember a version of this ceremony depicted in one of the later episodes, conducted by the hippo-headed Egyptian goddess of childbirth and fertility, Taweret.) Of the 192 spells currently known—no one manuscript contains them all—there are several protective spells to guard against the damage or loss of the heart, and in one case (30b) imploring the heart not to “betray” its owner during the weighing ritual by “telling lies in the presence of the god.”
Copies of the Book of the Dead were made to order by scribes, and the scrolls could be as short as 1 meter (3.2 feet) and as long as 40 meters (about 131 feet). People knew of the existence of such scrolls in the Middle Ages, and assumed that they were religious in nature because they were found in tombs. Karl Richard Lepsius coined the name Book of the Dead in 1842 after translating one such text. The best known example to date is the Papyrus of Ani, discovered in luxor in 1888 and now housed in the British Museum. But such finds are increasingly rare.