To cross a stream, highway or valley (where by the hold off brought on by a flight of locks at either facet would be unacceptable) the valley is usually spanned by a navigable aqueduct – a famous instance in Wales would be the Pontcysyllte Aqueduct (now a UNESCO Globe https://musica-infantil66543.mpeblog.com/65519963/the-definitive-guide-to-urso-fofo