The Greenwich meridian became the internationally adopted prime meridian in 1884.
Delegates at the International Meridian Conference in Washington, D.C., selected the meridian passing through the Royal Observatory at Greenwich as longitude zero. The conference took place in October 1884.
The decision reflected the widespread use of British nautical charts and the Greenwich meridian in navigation. It also established a common reference for measuring longitude east and west around the globe.
Modern geodesy uses the International Reference Meridian, which is about 102 metres east of the historic Greenwich line. However, Greenwich remains the familiar name associated with the prime meridian and Greenwich Mean Time.