To cross a stream, road or valley (where by the hold off due to a flight of locks at both aspect can be unacceptable) the valley can be spanned by a navigable aqueduct – a famous illustration in Wales will be the Pontcysyllte Aqueduct (now a UNESCO Planet Heritage https://canalinfantil99593.digiblogbox.com/61570304/considerations-to-know-about-urso-fofo