To cross a stream, road or valley (where by the hold off due to a flight of locks at both side would be unacceptable) the valley may be spanned by a navigable aqueduct – a famous case in point in Wales could be the Pontcysyllte Aqueduct (now a UNESCO https://ursofofo80998.jaiblogs.com/64083549/detailed-notes-on-musica-infantil