To cross a stream, road or valley (where the hold off because of a flight of locks at possibly aspect might be unacceptable) the valley is often spanned by a navigable aqueduct – a well known illustration in Wales would be the Pontcysyllte Aqueduct (now a UNESCO Planet Heritage https://lukasdmswa.affiliatblogger.com/89225076/detailed-notes-on-musica-infantil