Armies generally had to move over longer distances via roads, for both logistical and pathfinding reasons. For logistics, while unencumbered humans can easily clamber over fences or small ridges or weave through forests, humans carrying heavy loads struggle to do this and pack animals absolutely cannot. Dense forests (especially old growth forests) are formidable obstacles for pack and draft animals, with a real risk of animals injuring themselves with unlucky footfalls. After all the donkey was originally a desert/savannah creature and horses evolved on the Eurasian Steppe; dense forest is a difficult, foreign terrain. But the rural terrain that would dominate most flat, arable land was little better: fields are often split by fences or hedgerows which need to be laboriously cleared (essentially making a path) to allow the work animals through. Adding wagons limits this further; pack mules can make use of narrow paths through forests or hills, but wagons pulled by draft animals require proper roads wide enough to accommodate them, flat enough that the heavy wagon doesn’t slide back and with a surface that will be at least somewhat kind on the wheels. That in turn in many cases restricts armies to significant roadways, ruling out things like farmer’s paths between fields or small informal roads between villages, though smaller screening, scouting or foraging forces could take these side roads.

(As an aside: one my enduring frustrations is the tendency of pre-modern strategy games to represent most flat areas as “plains” of grassland often with a separate “farmland” terrain type used only in areas of very dense settlement. But around most of the Mediterranean, most of the flat, cleared land at lower elevations would have been farmland, with all of the obstructions and complications that implies; rolling grasslands tend to be just that – uplands too hilly for farming.)

The other problem is pathfinding and geolocation. Figuring out where you off-road overland with just a (highly detailed) map and a compass is sufficiently difficult that it is a sport (Orienteering). Prior to 1300, armies in the broader Mediterranean world were likely to lack both; the compass (invented in China) arrives in the Mediterranean in the 1300s and detailed topographical maps of the sort that hikers today might rely on remained rare deep into the modern period, especially maps of large areas. Consequently it could be tricky to determine an army’s exact heading (sun position could give something approximate, of course) or position. Getting lost in unfamiliar territory was thus a very real hazard. Indeed, getting lost in familiar territory was a real hazard: Suetonius records that Julius Caesar, having encamped not far from the Rubicon got lost trying to find it, spent a whole night wandering trying to locate it (his goal being to make the politically decisive crossing with just a few close supporters in secrecy first before his army crossed). In the end he had to find a local guide to work his way back to it in the morning (Suet. Caes. 31.2). So to be clear: famed military genius Julius Caesar got lost trying to find a 50 mile long river only about 150 miles away from Rome when he tried to cut cross-country instead of over the roads.

Instead, armies relied on locals guides (be they friendly, bought or coerced) to help them find their way or figure out where they were on whatever maps they could get together. Locals in turn tend to navigate by landmarks and so are likely to guide the army along the paths and roads they themselves use to travel around the region. Which is all as well because the army needs to use the roads anyway and no one wants to get lost. The road and path network thus becomes a vital navigational aid: roads and paths both lead to settlements full of potential guides (to the next settlement) and because roads tend to connect large settlements and large settlements tend to be the objectives of military campaigns, the road system “points the way”. Consequently, armies rarely strayed off of the road network and were in most cases effectively confined to it. Small parties might be sent out off of the road network from the main body, but the main body was “stuck” on the roads.

That means the general does not have to cope with an infinitely wide range of maneuver possibilities but a spiderweb of possible pathways. Small, “flying columns” without heavy baggage could use minor roads and pathways, but the main body of the army was likely to be confined to well-traveled routes connecting large settlements.

Bret Devereaux, “Collections: Logistics, How Did They Do It, Part III: On the move”, A Collection of Unmitigated Pedantry, 2022-08-12.