It seems from some offlist messages that my laconic numbers spread
across several message didn't form a comprehensive picture. I'll try
to correct that.
First I should mention that the average numbers for walking distance
per hour or per day are not desert specific. They are average
numbers, and as such they average the conditions too. They depend
more on human physiology than on topography or climate.
Example: Walking a level path in central Sinai in July will be
significantly harder than walking a much less level path along the
top of the central mountain range in Canaan (e.g. Jerusalem to
Shechem or Hebron). The situation will be reversed in April - the
Sinai walk will be pleasant while the mountain walk will be through
thick spring vegetation (no paved roads before the Romans). And the
July walk in Sinai will be significantly easier than a July walk on a
level path from Tiberias to Dan, because while the temperatures will
be in the same range, the high humidity in the upper Jordan basin
will increase the "heat factor" significantly.
A normal person will average in non extreme conditions 5 km/h and
will be able to go on indefinitely walking at such a speed for 10
hours a day carrying a light load (I think the figure for the load is
up to 20 kg). So the expression "a day's distance" or "a day's walk"
usually means (when it doesn't have a defined meaning for a specific
context) about 50 km (roughly 30 miles).
It may seem strange that this average speed works for most climates.
It seems obvious that walking a level path in a very hot desert is
much harder than walking a similar path in e.g. Holland. But when you
walk in the desert you'll split the 10 hours to the morning and
afternoon-evening and rest in the middle of the day - you'll still
get the same 10 hours of walking.
A specific context for which there is another figure is a large
infantry force, meaning hundreds or thousands or people with heavy
loads. The figure, from various armies across various periods and
geographical areas, is around 25 km/day. The more people you have the
wider the fitness range will be and the slowest person determines the
overall speed. The load carried by each person is significantly
heavier. Unless the route conditions are extremely favorable, such a
group will proceed as a single file column and the overall time will
be from the moment the first person leaves until the moment the last
person arrives. Etc.
At the other end of the distance-per-day range are "elite" walkers,
e.g. commandos. They can reach 100km/day. They do it both by walking
slightly faster (averaging maybe 6-7 km/h) and especially by walking
more hours per day. 16 hours per day at 6km/h is 96 km. This however
is not a speed that can be maintained indefinitely.
When a walking party includes pack animals it slows down and the
figure is about 25 km/day. Again it's an average and a lot will
depend on which animals are used. Humans are much more adaptable to
various terrain and weather conditions than pack animals - a donkey
is not adapted to sandy dunes and a camel is not adapted to mountain
passes. Caravans will be slower, but they won't need more watering
spots than a group of only humans walking at 50 km/day. The pack
animals can carry significantly more water than a person so that both
people and animals can proceed with watering stops every two days.
So for people-only and for caravans the distance between watering
"pit stops" that determines if a desert can be crossed is about 50km.
[Again, it's an average figure, a general indicator, that has to be
adapted to the specifics of each case. It shouldn't be used as a
magic number. For example walking dune "waves" length-wise is within
normal walking conditions but crossing those same dunes, i.e.
climbing dunes up and down, would be extreme walking conditions. It's
the same terrain, but the direction in which it is crossed will
determine the distance per day. When you look at a map it will be
obvious if the path is along a mountain ridge or crosses it, but a
map might fool you to think that crossing a dune area will be done at
the same speed in any direction]
Pit stops that are 50km apart are a problem for a large infantry
group proceeding at 25 km/day. In order to drink and refill every
other day each person will need to carry the extra day's water. That
will be about 10 kg added to an already heavy load. That would either
slow the speed per day even more, or require recuperation days at pit
stops. Adding pack animals is a partial solution, but if you have
thousands of soldiers you'll need hundreds of animals and every pit
stop will have to provide a lot more water. And even when the pit
stops are nearer to each other, what may be an adequate pit stop for
a caravan may not have enough water for thousands of men. And an army
can't reach its destination and ask the enemy to wait patiently
several days for the exhausted soldiers to recuperate ...
All this should be familiar to ANErs - people and caravans have
routinely crossed the NE deserts in various paths, but military
forces had a much more difficult time and were limited in their
choice of routes. E.g. practically all military expeditions to and
from Egypt used the "sea route" along the northern part of the Sinai
because it has a lot of watering pit stops, because the terrain is
mostly flat, and because the proximity of the sea makes the climate
more clement. The trade route going through central Sinai is a
perfectly good route for caravans but is practically impossible for
large infantry forces.
With livestock herds the desert crossing strategy, in the rare cases
when such a crossing must be done, is to force march them between
several pit stops and make a long recuperating stop at an oasis where
they have both water and food.
I hope this made the picture somewhat clearer.
[100% bona fide dilettante ... delecto ergo sum!]
Ariel L. Szczupak
AMIS-JLM (Ricercar Ltd.)
POB 4707, Jerusalem, Israel 91401
Phone: +972-2-5619660 Fax: +972-2-5634203