incorrect: units suffer heavy fatigue penalties when just walking uphill, especially in the steep mountains (like the Alps, Pyrenees, etc.)
woops, shold have mentioned steep terrain, I know for a fact though that walking across flat terrain DOES NOT tire them out because i've walked across a mostly level maps-width with no fatigue changes on simpile militia units, and they where in desert (one of the non-desert factions too so...).