Car Dyke
The 928th tallest dam in the world
The Car Dyke is a long ditch which runs along the western edge of the Fens in eastern England for a distance of over 57 miles (92 km). It is generally accepted as being a Roman construction and was, for many centuries, considered to mark the western edge of the Fens. Its name derives from carr, a fourteenth-century word for marsh or drained land.
Dam data from Wikidata (CC0) plus curated additions. Summary from Wikipedia (CC BY-SA).