The Greek historian Herodotus on the process of
mummification -- and he has been proven accurate:
The mode of embalming, according to the most perfect process, is the
following:- They take first a crooked piece of iron, and with it draw
out the brain through the nostrils, thus getting rid of a portion,
while the skull is cleared of the rest by rinsing with drugs; next they
make a cut along the flank with a sharp Ethiopian stone, and take out
the whole contents of the abdomen, which they then cleanse, washing it
thoroughly with palm wine, and again frequently with an infusion of
pounded aromatics. After this they fill the cavity with the purest
bruised myrrh, with cassia, and every other sort of spicery except
frankincense, and sew up the opening. Then the body is placed in natrum
for seventy days, and covered entirely over. After the expiration of
that space of time, which must not be exceeded, the body is washed, and
wrapped round, from head to foot, with bandages of fine linen cloth,
smeared over with gum, which is used generally by the Egyptians in the
place of glue, and in this state it is given back to the relations, who
enclose it in a wooden case which they have had made for the purpose,
shaped into the figure of a man. Then fastening the case, they place it
in a sepulchral chamber, upright against the wall. Such is the most
costly way of embalming the dead.
If persons wish to avoid expense, and choose the second process, the
following is the method pursued:- Syringes are filled with oil made
from the cedar-tree, which is then, without any incision or
disembowelling, injected into the abdomen. The passage by which it
might be likely to return is stopped, and the body laid in natrum the
prescribed number of days. At the end of the time the cedar-oil is
allowed to make its escape; and such is its power that it brings with
it the whole stomach and intestines in a liquid state. The natrum
meanwhile has dissolved the flesh, and so nothing is left of the dead
body but the skin and the bones. It is returned in this condition to
the relatives, without any further trouble being bestowed upon it.
The third method of embalming, which is practised in the case of the
poorer classes, is to clear out the intestines with a clyster, and let
the body lie in natrum the seventy days, after which it is at once
given to those who come to fetch it away.
Source: Herodotus, The History
Book 2, chapters 86-89