To cross a stream, highway or valley (where by the hold off a result of a flight of locks at possibly facet can be unacceptable) the valley could be spanned by a navigable aqueduct – a well known illustration in Wales may be the Pontcysyllte Aqueduct (now a UNESCO https://urso-fofo33321.link4blogs.com/58095467/the-best-side-of-urso-fofo