To cross a stream, highway or valley (wherever the hold off due to a flight of locks at both aspect 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 Entire https://damienwhnru.idblogmaker.com/36171383/new-step-by-step-map-for-urso-fofo