To cross a stream, highway or valley (where by the hold off due to a flight of locks at both side would be unacceptable) the valley can be spanned by a navigable aqueduct – a famous case in point in Wales is the Pontcysyllte Aqueduct (now a UNESCO Earth https://ursofofo90998.thezenweb.com/detailed-notes-on-musica-infantil-75338087