To cross a stream, road or valley (where the delay brought on by a flight of locks at either facet might be unacceptable) the valley is often spanned by a navigable aqueduct – a popular example in Wales will be the Pontcysyllte Aqueduct (now a UNESCO Entire world Heritage https://chancezejpt.activablog.com/36290632/the-2-minute-rule-for-urso-fofo