To cross a stream, highway or valley (in which the delay because of a flight of locks at both side could be unacceptable) the valley may be spanned by a navigable aqueduct – a well-known example in Wales is the Pontcysyllte Aqueduct (now a UNESCO World Heritage Web page) https://stepheniptzd.p2blogs.com/35822354/the-single-best-strategy-to-use-for-musica-infantil