To cross a stream, road or valley (wherever the hold off brought on by a flight of locks at either facet could be unacceptable) the valley might be spanned by a navigable aqueduct – a famed case in point in Wales could be the Pontcysyllte Aqueduct (now a UNESCO https://emilianosbhkn.widblog.com/91928732/considerations-to-know-about-canal-infantil