To cross a stream, road or valley (where the hold off caused by a flight of locks at possibly aspect can be unacceptable) the valley could be spanned by a navigable aqueduct – a well-known example in Wales will be the Pontcysyllte Aqueduct (now a UNESCO World Heritage Web https://musicainfantil79988.blogaritma.com/35275048/facts-about-urso-fofo-revealed