That's true for practically all military movement. The maximum speed of an individual man, horse or vehicle is purely theoretical for marching a military formation. Even under ideal conditions (i.e. without poor roads, hot weather, river fordings etc.), one has to allow for short breaks (Napoleon gave his men five minutes in the hour), for meals and generally for all sort of delays. And then there's the fact of life that formations march slower than individuals. Even a small group of four or five will be slower than a single man (ask any father about it [;)]) and a company or battalion, let alone a brigade or division, simply cannot count on normal walking speed. 15 miles is a good day's work for a division; Prussian army regulations allowed for three German miles (22.5 kilometers) per day, but with a full day of rest on every fourth day. Of course one could order a forced march, but only at the price of a badly increased number of footsores and stragglers, not to mention reduced overall performance in battle if it ensued right after the march.
And that's men. Now horses is an entirely different matter again because, paradoxical as it may sound, they break down a lot easier than men and have to be cared for a lot more. That's why cavalry moves at a trot <u>even in a charge</u> except maybe in the last few moments. Regulations for cavalry charges may have stated that the speed should be gradually increased to full gallop but quite often (for instance that's true for most French charges at Waterloo) the horses were simply too tired for that.
The fact is simply that in the field you can work men harder than horses and still keep them going for days on end. Off the road, good infantry could outpace cavalry, even light cavalry. Operationally, there should be very little difference between the speed of infantry and cavalry. Tactically, maybe some. In the BG games, where you have to count the movement and the charge allowance combined, I think with twice the infantry allowance it's probably too much. In HPS Eckmuhl and Wagram I believe infantry moves five hexes tactically and cavalry seven--that seems about right to me. (Especially considering that elevation changes slow down cavalry only.)
<center>Général de Division D.S. "Green Horse" Walter
Baron d'Empire, Duc des Pyramides
Commandant de la [url="http://home.arcor.de/dierk_Walter/NWC/3_VI_AdR_Home.htm"]3ème Division[/url], VIème Corps Bavarois, L'Armée du Rhin
Commandant l'Ecole de Mars, L'Armée du Rhin
Commandant de la Brigade de Tirailleurs de la Jeune Garde

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