Distance marching rates, infantry v cavalry

[Vindex]

Remounts would be required but, as far as I'm aware, we don't know how many. However, I expect that the majority of the remounts marched with the legionaries - probably with a nose-bag stuffed with hay! - and this negates the need for the patrolling cavalry to tend for the remounts.

Regards, Steve

Hate to be a bit nit picky but if you put hay in a bag under the horse's nose you'll probably suffocate it. Grain, yes; hay no. And I'm not sure if horses would eat on the march in this manner...but as they graze and chew there's no real reason why not. If they're hungry enough I'm sure they would!

As for a central cavalry reserve; it makes strategic sense to have a reserve or units on call which can provide the sort of rapid reaction force you are talking about. But as with your York to the Wall scenario, it isn't inconceivable. There would be remounts available from more local units and an unridden, led horse will be less tired than a ridden horse so you could take one with you, dropping off the tired one at a convenient mansio on the way through.