To cross a stream, street or valley (in which the hold off due to a flight of locks at either side would be unacceptable) the valley is usually spanned by a navigable aqueduct – a famed illustration in Wales is the Pontcysyllte Aqueduct (now a UNESCO World Heritage Website) https://jaidenhqwad.jiliblog.com/93559374/musica-infantil-for-dummies