To cross a stream, highway or valley (exactly where the delay due to a flight of locks at both aspect will be unacceptable) the valley could be spanned by a navigable aqueduct – a famed illustration in Wales could be the Pontcysyllte Aqueduct (now a UNESCO Globe Heritage Web https://urso-fofo22109.diowebhost.com/92133705/the-canal-infantil-diaries