Romans also lined their aqueducts with concrete of a much better grade than we use. it was waterproof, and even could set under water. They also could make water run up hill without pumps*! Concrete (and stone) is crap in tension, so they always designed their buildings so concrete was never in tension. Our 'modern' re-enforced concrete usually only lasts a few decades, water seeps in and rusts the rebar. rust takes up more room than steel, so internal pressures crack the concrete, and it eventually fails. The Parthenon in Rome has been around for a couple millenia, it's huge concrete dome has NO rebar, and we'd struggle to duplicate it and it's life even now.
They were quite aware that too steep an incline of the duct was as bad as too shallow. Too shallow, not enough flow, too steep and water velocity for the desired flow rate can increase pressures in directional changes. The water effectively jamming or blowing out the system. They also covered the ducting to prevent evaporation. They also tunnelled through rock from both sides, usually meeting with very little offset (but not always!)
*-
http://www.romanaqueducts.info/pictu...pen/siphon.htm
p.s.- Fernandos example could use a wheel on the chape drag
