To cross a stream, highway or valley (where by the hold off due to a flight of locks at either side could be unacceptable) the valley can be spanned by a navigable aqueduct – a famed case in point in Wales would be the Pontcysyllte Aqueduct (now a UNESCO https://musicainfantil98775.daneblogger.com/36048280/facts-about-urso-fofo-revealed