To cross a stream, highway or valley (wherever the delay brought on by a flight of locks at either facet can be unacceptable) the valley is often spanned by a navigable aqueduct – a well known example in Wales is definitely the Pontcysyllte Aqueduct (now a UNESCO Globe Heritage https://urso-fofo67654.blogrelation.com/43502668/details-fiction-and-canal-infantil