I have a world that isn't an exact analogue to medieval technology, closer to the late 1700s in terms of culture and agriculture/metallurgy, only without gunpowder. I have them ahead of real history for this time period in some areas (e.g., medical and farm science), but behind in others (notably military science, they still use enlightenment style militaries - pikemen, heavy cavalry, medieval-style ballistae and trebuchets, crossbows, etc). I have been thinking of a system for rapid mass transit over land and wanted to find out if it was feasible as a replacement for trains as internal combustion engines will not be present in this world for various handwave-y reasons.
Here's what I'm thinking: The fastest and most efficient form of travel before engines was boats - rivers were the primary way to ship things in bulk with any speed over continents, and ocean going vessels are much faster oftentimes than traversing the inland of a continent on foot/horse, even if you end up going way more miles roundabout. So, I have an empire that wishes to build artificial rivers of a sort in order to facilitate this fast travel, connecting their cities. I imagine massive raised aqueducts 100m in width and a few tens of meters in depths. Through a massive set of pumps powered by manual labor / ox teams / wind power, huge amounts of water are pumped up to fill the aqueduct for miles and miles.
The aqueducts are split into half, and each half has a slightly opposite slope: so that the water flows in one direction on each half, so even unpowered ships can just float down the aqueduct to their destination, though oars/sail are typically used to increase the speed. The slope is just slight enough to get the water moving, it doesn't have to be a large incline. The aquifers are raised so that if for instance the destination city is at a higher altitude than the source city, the aqueduct at the source is still higher to maintain that incline. Ignore problems associated with moving cargo up and down these aqueducts.
Assume almost unlimited manpower / political will to accomplish this. Is this a feasible engineering feat for this general level of tech? I imagine the aqueducts will be made from something akin to concrete joining large cut stone blocks but am open to suggestions. My only rule is no gunpowder/combustion engines.