To cross a stream, street or valley (where the hold off brought on by a flight of locks at possibly facet can be unacceptable) the valley can be spanned by a navigable aqueduct – a well-known example in Wales is definitely the Pontcysyllte Aqueduct (now a UNESCO World Heritage https://dallasluzgj.thekatyblog.com/35633128/new-step-by-step-map-for-urso-fofo