To cross a stream, highway or valley (wherever the hold off attributable to a flight of locks at both aspect could be unacceptable) the valley can be spanned by a navigable aqueduct – a famous case in point in Wales could be the Pontcysyllte Aqueduct (now a UNESCO Earth https://kylerdmswa.diowebhost.com/92137403/top-guidelines-of-urso-fofo