Linked from
The 10 pages that link to Prime meridian, each with the reason it gives.
LongitudeRelated: Longitude is measured east or west from this zero line.
Geographic coordinate systemRelated: It establishes the reference from which longitude is measured.
HemisphereRelated: Together with the 180th meridian, it defines the eastern and western hemispheres.
180th meridianRelated: The 180th meridian lies directly opposite this longitude reference.
Eastern HemisphereRelated: It marks the western boundary of the Eastern Hemisphere.