To cross a stream, road or valley (where the hold off because of a flight of locks at possibly facet can be unacceptable) the valley might be spanned by a navigable aqueduct – a renowned example in Wales will be the Pontcysyllte Aqueduct (now a UNESCO Earth Heritage Web https://musica-infantil73715.p2blogs.com/35818728/what-does-canal-infantil-mean