A rose line, also called a meridian or longitude, is any line

from the North to South poles. Early navigators had to

choose which of these lines would be the Rose Line, the zero longitude. Today that line is in Greenwich, England. But 135 brass Arago markers set into the streets of Paris, France mark the world's

first prime meridian.

The original Rose Line passes through many secular and sacred landmarks. Embedded in the floor of the famous church of

Saint-Sulpice, a thin polished strip of brass glistens and

crosses the floor, slices the main altar, cleaves the communion rail,

and arrives at the base of an ancient Egyptian obelisk.

The line bears graduated markings, like a ruler.