To cross a stream, road or valley (wherever the hold off due to a flight of locks at both side would be unacceptable) the valley is usually spanned by a navigable aqueduct – a well-known example in Wales is definitely the Pontcysyllte Aqueduct (now a UNESCO Earth Heritage Internet https://canalinfantil56654.collectblogs.com/81782013/the-2-minute-rule-for-urso-fofo