In the history of Rome there are numerous instances of legions being marched up and down Europe, from Spain to Rome and from Rome to Syria. I'm interested to know how quickly these armies could move? Did it take a half a year to move from the Alps to Rome or did it take a week?
Also how does that speed compare to the pace of the mobile cavalry reserve used to such great effect by the late Roman emperors?
This (fun) site assumes 10 miles per day, while adding the necessary disclaimer "it depends".
However, I was not able to confirm this number in the cited source: John Pebbie's The Roman War Machine seems to refer to "10 miles" only in specific relation to a march undertaken by Caesar's army on its final approach to the Battle of Sabis.
The same book contains several concrete numbers (including references to primary sources) for speeds perhaps achievable by the Roman postal service and by individuals traveling on important missions. Here is an example:
Plutarch relates that Julius Caesar on one occasion travelled 100 miles a day for eight days in succession, driving in a hired raeda.
It relates that cavalry ("widely deployed in a protective screen around the army on the march, and penetrating deeper into the surrounding countryside") could have covered 40 miles a day. It also quotes Vegetius (5th century CE) on the practice of training marches with complete armor over distances of ten miles from a camp plus return:
Decem milia passuum armati instructique omnibus telis pedites militari gradu ire ac redire iubebantur in castra ...
And FYI, here is a later account (again from Andrew Wheatcroft's The Enemy at the Gate: Habsburgs, Ottomans, and the Battle for Europe) that quantifies daily distances traveled by an Ottoman army in the 17th century:
The whole force could advance only at the pace of ox carts and the cannon, perhaps twelve miles a day.
From the Summary in Observations on marching Roman Legionaries ..
I know this is an old question but I think there is a really good tool that is not mentioned here. There is a comprehensive model that was created by Stanford to model how long travel took in Roman times, since you are interested in Military be sure to set your options correctly, under Mode Foot be sure to select Rapid Military March (or Ox-Cart or whatever depending on the armies method of travel,) also Select River and change to Military. This model allows for so many variables including type of march, season of march, method of transport. It will give you a very good approximation of the travel time from different cities in the Empire.
Scipio Africanus legions marched on an average of 26 miles / day to get from Tarraco to Carthago Nova in 6 days, but those are extreme numbers on a very forced speed, usually, it would be half that amount.
John Harrel in "The Nisibis War" uses an estimate of 10 miles per day -- roughly 16km a day -- for "normal" conditions. They could go faster, at the cost of exhaustion or a less well-developed camp, or they could go slower, if conditions like heat or terrain forced them.
One of the interesting facts is that a large enough force would have the vanguard and scouts setting up the next camp before the rear guard left the previous camp!
The question is how quickly could Roman legions move? Well a single soldier in the modern U.S army is required to complete a Loaded March, carrying weight of up to 70 pounds, of 12 miles in less than 3 hours to attain an Expert Infantryman Badge. The 'Raid March' practised by the French Foreign Legion requires a march of 75 miles in 3 days in full combat gear carrying rifle and 70 pounds of gear. A Full Pace march for a Roman Legionary in basic training required a march in daylight hours of 22 miles. Clearly it is entirely possible a Roman Legion could march 20-30 miles per day if needed. It is well documented Roman soldiers never stopped training during their 25 year service and it may well be a mistake to underestimate the fitness and endurance of a Roman soldier compared to that of a modern soldier especially given the only mode of troop movement available to a Roman foot soldier was the march.
