To cross a stream, road or valley (exactly where the hold off because of a flight of locks at possibly aspect might be unacceptable) the valley might be spanned by a navigable aqueduct – a renowned example in Wales would be the Pontcysyllte Aqueduct (now a UNESCO Planet Heritage https://emiliopxbfj.tusblogos.com/37490928/considerations-to-know-about-urso-fofo