To cross a stream, road or valley (wherever the hold off because of a flight of locks at both facet would be unacceptable) the valley could be spanned by a navigable aqueduct – a famed case in point in Wales is the Pontcysyllte Aqueduct (now a UNESCO Environment Heritage https://urso-fofo64284.link4blogs.com/58103733/5-easy-facts-about-musica-infantil-described