To cross a stream, road or valley (exactly where the hold off caused by a flight of locks at either side might be unacceptable) the valley is often spanned by a navigable aqueduct – a well known instance in Wales could be the Pontcysyllte Aqueduct (now a UNESCO World https://ursofofo42848.blogthisbiz.com/44278265/top-guidelines-of-urso-fofo