To cross a stream, road or valley (wherever the hold off due to a flight of locks at both side could be unacceptable) the valley can be spanned by a navigable aqueduct – a famed example in Wales is the Pontcysyllte Aqueduct (now a UNESCO World Heritage Web page) https://glucotrust-pills00976.creacionblog.com/36911253/everything-about-urso-fofo