To cross a stream, highway or valley (the place the delay brought on by a flight of locks at both facet will be unacceptable) the valley may be spanned by a navigable aqueduct – a famed illustration in Wales would be the Pontcysyllte Aqueduct (now a UNESCO Planet Heritage https://urso-fofo33210.idblogmaker.com/36161461/details-fiction-and-canal-infantil