To cross a stream, highway or valley (where the hold off a result of a flight of locks at either aspect would be unacceptable) the valley is often spanned by a navigable aqueduct – a famed example in Wales could be the Pontcysyllte Aqueduct (now a UNESCO Earth Heritage https://musica-infantil88779.blogdomago.com/35925118/helping-the-others-realize-the-advantages-of-urso-fofo