"Most Difficult to Traverse?" Topic

How big is the desert? How high the mountain chain? Are there any roads? A river you can cross, though it might take time.

Do I have boats? A pontoon train? Do the mountains contain hostile troops? Are there oases in the desert? Do I know where they are? And can they quench my army's thirst? For that matter, how wide is it? Can I carry enough water to cross?

I don't think there's a useful abstract answer: only one in particular circumstances.

It also depends on which Napoleonic-era (by which, I assume you mean forces engaged in European style large army force-on-force combat during that period) force you are talking about.

It depends on a multitude of factors.

A large river defended by a determined opponent is very hard. A mountain chain in winter without low passes is brutal. A wide desert is a killer

too many factors to consider in each case.

I seem to remember a bit in Clausewitz to the effect that the defense of rivers--and possibly mountain ranges?--was purely a function of the defender's troop density. If the defender could put enough force in place at potential crossing points, it didn't matter how many men the attacker had. But if the defender was stretched too thinly, even an outnumbered attacker could make the crossing. It might be a foolish thing to do, but it could be done.

I read a book a couple of years back entitled "With the guns in the Peninsula" or something like.

Anyway, it was the diaries of an artillery officer. He reckoned mountains were the absolute worst terrain to get guns across. So I went with his professional opinion…

I think large bodies of water such as seas and ocean are the definitive answer.

Bridging a river takes some material but while I never had reads its easy.
Deserts are harder in you need to take everything with you.
Mountains maybe

I thought a ridge in Belgium