To cross a stream, highway or valley (where by the hold off due to a flight of locks at either side could be unacceptable) the valley could be spanned by a navigable aqueduct – a famous case in point in Wales is definitely the Pontcysyllte Aqueduct (now a UNESCO https://ursofofo85173.blogchaat.com/37295962/the-fact-about-musica-infantil-that-no-one-is-suggesting