Peacehaven Meridian Monument

At this point on the British Channel coast, the prime meridian leaves England to meet the European mainland in Villers-Sur-Mer (Normandy) in France. It is an imaginary border line that - starting from the London district of Greenwich, where the heart of the British Navy has beaten for centuries and where the Royal Observatory was located - circles the globe and includes the division into eastern and western longitudes. The ability to navigate using the exact determination of longitude and latitude was an epochal milestone in seafaring.
A film contribution (in German) from the series "Treasures of the World - Heritage of Humanity" explains the facilities in Greenwich, which are part of the UNESCO World Heritage Site, and discusses the problem of longitude measurement that was solved there. The film can be found in the ARD media library at the following link
ardmediathek.de/video/schaetze-der-welt/maritime-greenwich-grossbritannien-folge-194/swr/Y3JpZDovL3N3ci5kZS83MDM1NjMw