To cross a stream, highway or valley (in which the delay brought on by a flight of locks at either aspect will be unacceptable) the valley could be spanned by a navigable aqueduct – a popular instance in Wales is the Pontcysyllte Aqueduct (now a UNESCO Environment Heritage Web-site) https://musica-infantil11009.laowaiblog.com/36020071/new-step-by-step-map-for-urso-fofo