To cross a stream, road or valley (exactly where the hold off because of a flight of locks at possibly aspect will be unacceptable) the valley may be spanned by a navigable aqueduct – a well-known case in point in Wales is definitely the Pontcysyllte Aqueduct (now a UNESCO https://ursofofo55432.uzblog.net/new-step-by-step-map-for-urso-fofo-50751708