To cross a stream, street or valley (in which the delay due to a flight of locks at possibly facet could well be unacceptable) the valley can be spanned by a navigable aqueduct – a well known case in point in Wales would be the Pontcysyllte Aqueduct (now a https://urso-fofo56542.tinyblogging.com/urso-fofo-things-to-know-before-you-buy-80933797