To cross a stream, street or valley (in which the hold off attributable to a flight of locks at both side will be unacceptable) the valley could be spanned by a navigable aqueduct – a renowned example in Wales will be the Pontcysyllte Aqueduct (now a UNESCO World Heritage https://manueleotxb.onesmablog.com/little-known-facts-about-musica-infantil-77986043