To cross a stream, street or valley (where by the hold off attributable to a flight of locks at both aspect can be unacceptable) the valley might be spanned by a navigable aqueduct – a famed case in point in Wales will be the Pontcysyllte Aqueduct (now a UNESCO https://musica-infantil97393.bloggazza.com/36073816/the-definitive-guide-to-urso-fofo