In the 1990s the Dutch artist Jan Dibbets was commissioned to create a monument to the nineteenth-century astronomer François Arago, who extended the Paris meridian to the south. Dibbets's monument is a series of 135 medallions along the Paris stretch of the meridian, set into sidewalks, roads, and even some buildings (the Observatory, the Louvre, and the Palais Royal). On the Thursday holiday I followed part of the meridian, trying to spot as many of the medallions as possible.