To cross a stream, highway or valley (exactly where the delay caused by a flight of locks at both side could be unacceptable) the valley can be spanned by a navigable aqueduct – a famed case in point in Wales could be the Pontcysyllte Aqueduct (now a UNESCO Entire https://keeganirwad.smblogsites.com/37158419/detailed-notes-on-musica-infantil