To cross a stream, highway or valley (in which the hold off due to a flight of locks at either side will be unacceptable) the valley is usually spanned by a navigable aqueduct – a well-known illustration in Wales could be the Pontcysyllte Aqueduct (now a UNESCO Earth Heritage https://canalinfantil33210.blogadvize.com/45058711/little-known-facts-about-musica-infantil