Rick's doing more of the research on this project than I have so I'll let him correct me but I believe most of the Roman roads in Gaul came well after Caesar's time. There were the Via Aquitania and Via Domitia in the already Roman controlled south but I don't believe they played a particular role in Caesar's campaigns so at this point we don't have plans to implement military roads in Rome. However, as you noted Caesar was famous for showing up when the Gauls and Germans least expected him and we do plan to highlight that through new bridge building and forced marching features.

Supply lines will still exist similarly to PoM/Gold for moving resources around the map but they'll be a little more flexible now since you'll be able to branch them by building supply camps out in the field.

Supply Camps?

One of the new features in Rome is the ability to build camps/forts out in the field and you'll be able to connect supply lines to these dynamic camps. I can't get into a lot of detail right now as we're still playtesting some of these things but stay tuned as we'll be releasing a lot more info on the new features in Rome in the coming weeks/months.

In the game system that we're developing for our Hegemony series, we've been trying to combine strategy, tactics and logistics on one continuous map, with the emphasis on the importance of reconnaissance, skirmishes and the many, many, many small engagements that occurred for every large, documented "historic" battle.

To emphasize strategy, you need a relatively discrete system of interconnected nodes (cities, towns, forts, camps, etc.), where units and food can be stockpiled. Units are then either left to defend, or deployed from those nodes. In a pure strategic system, battles can be abstracted.

To emphasize tactics and multiple small engagements, you need freedom for units to deploy and fight at any location while moving, with the ability to withdraw or add units to any engagement, dependent on a units ability to "get there on time". Although, getting there on time is also a strategic element.

To emphasize logistics, you need a bit of both; nodes to create stockpiles in, as well as unit food consumption and the ability to modify unit consumption through foraging, etc.

Roads are a strategic element and can easily reduce flexibility. So, how do we maintain the core concept of a large, zoomable, open map, with flexible tactics and still have a meaningful network of roads? At one extreme, we could leave roads as map "window dressing" to add some historical flavor. At the other extreme, movement could be restricted to a network of roads. Neither extreme works for Hegemony.

In Philip we looked at a number of ways to have units move faster on roads, but in the end, left roads to represent trade (gold generation and food redistribution).

A road system modeled along the lines of those old pneumatic tube systems might be interesting? But, there are problems with that system too.

Have you considered having something similar to a stance toggle similar to the current Philip version of a 'Camp' mode?

One of the other underutilized features in PoM/Gold that we're working on improving in Rome is the formation system which in Rome will have additional properties beyond a units position on the battlefield. For example, rather than the simple column formation in PoM/Gold, in Rome you'll have something like a forced march formation that has various trade offs to speed, supply capacity and combat ability.