To cross a stream, highway or valley (wherever the hold off due to a flight of locks at both side would be unacceptable) the valley is often spanned by a navigable aqueduct – a renowned case in point in Wales could be the Pontcysyllte Aqueduct (now a UNESCO Earth https://hectorltxcg.loginblogin.com/44898507/not-known-details-about-urso-fofo