To cross a stream, highway or valley (where by the hold off attributable to a flight of locks at both side might be unacceptable) the valley is often spanned by a navigable aqueduct – a well known example in Wales may be the Pontcysyllte Aqueduct (now a UNESCO Planet https://finnjjdws.bcbloggers.com/36192741/musica-infantil-can-be-fun-for-anyone