To cross a stream, highway or valley (the place the hold off because of a flight of locks at both side would be unacceptable) the valley can be spanned by a navigable aqueduct – a well-known case in point in Wales could be the Pontcysyllte Aqueduct (now a UNESCO https://canal-infantil12109.thezenweb.com/5-essential-elements-for-musica-infantil-75344458