To cross a stream, road or valley (in which the hold off caused by a flight of locks at either side would be unacceptable) the valley can be spanned by a navigable aqueduct – a famed example in Wales would be the Pontcysyllte Aqueduct (now a UNESCO Earth Heritage https://esteiraergomtricakikos26037.like-blogs.com/36866060/the-single-best-strategy-to-use-for-musica-infantil