To cross a stream, road or valley (in which the delay brought on by a flight of locks at either facet could well be unacceptable) the valley is often spanned by a navigable aqueduct – a well known illustration in Wales could be the Pontcysyllte Aqueduct (now a UNESCO https://travispyhat.post-blogs.com/57847361/the-single-best-strategy-to-use-for-musica-infantil