Hadrian wall, Big Wall, military roads, canals.

[Lazy sweeper]

The idea is to make this defence constructions behave like real walls, like city walls, and enhance mobility as they were military roads. Big wall of China and Hadrian wall should behave like that. Even without units guarding it they should keep hostiles off the borders. They should not be an easy pillage also.

Trade roads are affecting gameplay, because if you wish to leave a forest region from be penetrated, or a desert, from anyone, you can't. When a foreign trader enter your territory, it should ask permission to build a road. This has important military implications. Lack of mobility and late game supply tactics, when railroads should pop in, make the game feel too horizontal.
If I have One army of Archers, I need to defend from barbarians, and have 50 exes of borders to cover, speed is important, and normal trade roads just dont fit it.

Romans roads were military roads. Silk roads were not. Canals were roads.
England. The Netherland. China and south east asia have tons of canals. Canals apart, military roads
can allow the movement of large armies. See Napoleon in Russian winter, decimated for lack of fast transport out of injured/Miasma/Scurvy/wet feet/lack of supply. Same for Romans in the Black Forest..

Early engineers could make it, not without stone, in reasonable amount. With at least 20 charges, and maybe need three for build on hills, forests and swamps.

 

[MaryKB]

You can pillage roads to destroy them. I feel it is a bit of immersion to think that if we don't want someone doing something in our territory, we have to actively do something about it. We could say "Don't build those roads!", and then cay say "Oh yeah try and stop me!", and then we have to do it, and we can! In the real world that's what we'd have to do.

The Great Wall of China was not built to keep people out, but rather to make escape more difficult. I believe that was how it was designed in Civilization 5! There is a saying that "A wall is only as strong as the people defending it" (Eddard Stark I believe), so I think it makes sense that an empty wall should really do nothing.

I do wish there was an ability to construct canals! I feel this is something that has been lacking from the game for some time.