The site chosen for this, the first purpose built scientific building in England, was on a hill in the royal park at Greenwich, then a town outside London. Robert Hooke started work on a design for the observatory, possibly consulting Christopher Wren with whom he collaborated on several projects (and who is identified as the designer of the observatory in some accounts). On 10th August 1675, work was ready to begin and Flamsteed laid the foundation stone for the observatory.
Successive, royal astronomers used this building, later known as Flamsteed House, as the point from which they measured the longitude (distance east or west in degrees) of various places. In the nineteenth-century, an international convention agreed that the building should mark the Prime Meridian, that is zero degrees longitude. The Royal Observatory also became the ‘home’ of Greenwich Mean Time, initially the standard time for all British naval ships, and later the standard by which all clocks were set with variations according to time-zone.
The Royal Observatory is now a World Heritage Site administered by the National Maritime Museum.