To cross a stream, highway or valley (where by the hold off due to a flight of locks at both facet might be unacceptable) the valley is often spanned by a navigable aqueduct – a popular illustration in Wales could be the Pontcysyllte Aqueduct (now a UNESCO Earth Heritage https://canal-infantil12110.tblogz.com/rumored-buzz-on-canal-infantil-50442723