Ancient Egyptian religion held that a person's continued existence after death depended on the preservation of key elements of the self, among them the ka, a kind of life force or double, and the ba, a personal aspect often depicted as a bird with a human head, both of which were understood to need a recognisable, intact body to which to return, which is the theological premise that made mummification a religious necessity rather than an aesthetic preference. The classical process, developed over many centuries from simpler beginnings, removed the internal organs, which were preserved separately, often in canopic jars each assigned to a protective deity, while the heart was in most periods deliberately left in place, since it was regarded as the seat of thought and moral judgement and was required intact for the weighing of the heart in the afterlife.
The body was then dried using natron, a naturally occurring salt, over a period ancient sources and modern research both place at roughly seventy days, before being wrapped in many layers of linen, often interleaved with protective amulets, and placed in one or more nested coffins. The rites accompanying this process were themselves religious acts, performed by trained priests, one of whom traditionally wore the jackal mask of Anubis, the god most closely associated with embalming and the protection of the dead.