According to AcoUP, transport cost over land is five times that over rivers, and twenty times that over sea.
https://acoup.blog/2019/07/19/the-lonely-city-part-ii-real-c...
https://acoup.blog/2019/07/19/the-lonely-city-part-ii-real-c...
Rome and the Middle Ages both had a systems of canals which are neutral to navigate. They always require something to pull, but there isn’t any current.