The term "dark ages" was used to refer to how we (i.e. people in the present/historians) didn't have a lot of info about that period. As in, something dark is something you can't see into very well. The ages indeed weren't dark themselves though, that's a misunderstanding of the term and that misconception is exactly why historians try to avoid the term nowadays.
Roads were primarily built for military use, but once they were built anyone travelling on foot would benefit from them, which meant had real economic impacts. That said, boats can carry far more goods than pack mules far faster, and don't eat a ton of fodder every day. There's a reason all the big old cities are on rivers. It's also why the Roman empire was primarily on the Mediterranean.
Roads were primarily built for military use, but once they were built anyone travelling on foot would benefit from them, which meant had real economic impacts. That said, boats can carry far more goods than pack mules far faster, and don't eat a ton of fodder every day. There's a reason all the big old cities are on rivers. It's also why the Roman empire was primarily on the Mediterranean.
If anyone wants to read pages and pages of info about classical-era and roman roads, I recommend https://acoup.blog/2023/06/02/collections-roman-roads/