In the seventeenth century, the Kingdoms of France and England were major rivals in international maritime affairs. Both had significant navies and merchant marines and ships of both nations sailed the world’s oceans. Both nations also had excellent cartographers, producing charts used by their vessels and the vessels of many other nations. In 1666, King Louis XIV commissioned the construction of a national observatory to be located just outside Paris. One of the principal missions of the new observatory was to accurately measure the longitude (a major undertaking in those days) of charted locations. In 1667, members of the French Academy of Science laid out the site of the observatory adjacent to the Port Royal abbey outside Paris. Dedicated astronomer and Abbé Jean Picard marked the meridian through the center of the planned structure. The observatory was to be known as the Paris Observatory and the meridian marked by Abbé Picard would be known as the Paris meridian. It would be used as the prime meridian by French cartographers for more than 200 years. The Paris meridian was recalculated with greater precision by astronomer François Arago in the early 1800s. In 1994, medallions (bearing Arago’s name) were placed in Paris marking the route of the meridian. The cartography rivalry between France and Great Britain came to a head at the 1884 International Meridian Conference in Washington, DC. There, a large majority of the participating States adopted the Greenwich meridian as the world’s prime meridian, defeating others under consideration including Lisbon, Cadiz, Antwerp, Copenhagen, Berlin, Rome, Stockholm, Saint Petersburg, Tokyo, and Rio de Janeiro. France, joined only by Brazil, abstained. Use of the Paris meridian on French navigational charts continued until 1914. The Paris meridian (and the cartographic competition with the Greenwich meridian) is mentioned in Jules Verne’s “20,000 Leagues under the Sea”. Most prominently, the Paris meridian, renamed the Rose Line, is a major plot element in Dan Brown’s novel “The Da Vinci Code”. Since publication of the book and release of the motion picture, the line of Arago medallions has become a minor tourist attraction in Paris. While some in France still assert that the Paris meridian is at 0°, for international purposes, it is located at 2°20’14.025”E.