To cross a stream, highway or valley (wherever the hold off caused by a flight of locks at possibly aspect could be unacceptable) the valley can be spanned by a navigable aqueduct – a famous instance in Wales will be the Pontcysyllte Aqueduct (now a UNESCO Globe Heritage Site) https://musica-infantil88779.blogdomago.com/35925118/helping-the-others-realize-the-advantages-of-urso-fofo